Background reduction apparatuses and methods of ocular surface interferometry (osi) employing polarization for imaging, processing, and/or displaying an ocular tear film

ABSTRACT

Background reduction apparatuses and methods of Ocular surface interferometry (OSI) employing polarization are disclosed for measuring a tear film layer thickness (TFLT) of the ocular tear film, including lipid layer thickness (LLT) and/or aqueous layer thickness (ALT) and can be used to evaluate and potentially diagnosis dry eye syndrome (DES). In certain disclosed embodiments, a multi-wavelength light source can be controlled to illuminate the ocular tear film. Light emitted from the multi-wavelength light source undergoes optical wave interference interactions in the tear film. An imaging device can be focused on the lipid layer of the tear film to capture optical wave interference interactions of specularly reflected light from the tear film combined with a background signal(s) in at least one image. The at least one image can be processed and analyzed to measure a tear film layer thickness (TFLT), including lipid layer thickness (LLT) and/or aqueous layer thickness (ALT).

PRIORITY APPLICATIONS

The present application claims priority to U.S. Provisional Patent Application No. 61/638,260 entitled “BACKGROUND REDUCTION APPARATUSES AND METHODS OF OCULAR SURFACE INTERFEROMETRY (OSI) EMPLOYING POLARIZATION FOR IMAGING, PROCESSING, AND/OR DISPLAYING AN OCULAR TEAR FILM,” filed Apr. 25, 2012 which is incorporated herein by reference in its entirety.

The present application is a continuation-in-part application of U.S. patent application Ser. No. 12/798,325 entitled “OCULAR SURFACE INTERFEROMETRY (OSI) METHODS FOR IMAGING, PROCESSING, AND/OR DISPLAYING AN OCULAR TEAR FILM,” filed Apr. 1, 2010, which claims priority to U.S. Provisional Patent Application No. 61/211,596 entitled “OCULAR SURFACE INTERFEROMETRY (OSI) DEVICES, SYSTEMS, AND METHODS FOR MEASURING TEAR FILM LAYER THICKNESS(ES),” filed on Apr. 1, 2009, which are both incorporated herein by reference in their entireties.

RELATED APPLICATIONS

The present application is related to concurrently filed U.S. patent application Ser. No. ______ entitled “APPARATUSES AND METHODS OF OCULAR SURFACE INTERFEROMETRY (OSI) EMPLOYING POLARIZATION AND SUBTRACTION FOR IMAGING, PROCESSING, AND/OR DISPLAYING AN OCULAR TEAR FILM”, filed on Apr. 25, 2013, which claims priority to U.S. Provisional Patent Application No. 61/638,231 entitled “APPARATUSES AND METHODS OF OCULAR SURFACE INTERFEROMETRY (OSI) EMPLOYING POLARIZATION AND SUBTRACTION FOR IMAGING, PROCESSING, AND/OR DISPLAYING AN OCULAR TEAR FILM,” filed on Apr. 25, 2012, both of which are incorporated herein by reference in their entireties.

The present application is related to U.S. patent application Ser. No. 11/820,664 entitled “TEAR FILM MEASUREMENT,” filed on Jun. 20, 2007, issued as U.S. Pat. No. 7,758,190, which is incorporated herein by reference in its entirety.

The present application is also related to U.S. patent application Ser. No. 11/900,314 entitled “TEAR FILM MEASUREMENT,” filed on Sep. 11, 2007, issued as U.S. Pat. No. 8,192,026, which is incorporated herein by reference in its entirety.

The present application is also related to U.S. patent application Ser. No. 12/798,275 entitled “OCULAR SURFACE INTERFEROMETRY (OSI) DEVICES AND SYSTEMS FOR IMAGING, PROCESSING, AND/OR DISPLAYING AN OCULAR TEAR FILM,” filed on Apr. 1, 2010, which is incorporated herein by reference in its entirety.

The present application is also related to U.S. patent application Ser. No. 12/798,326 entitled “OCULAR SURFACE INTERFEROMETRY (OSI) METHODS FOR IMAGING AND MEASURING OCULAR TEAR FILM LAYER THICKNESS(ES),” filed on Apr. 1, 2010, issued as U.S. Pat. No. 8,092,023, which is incorporated herein by reference in its entirety.

The present application is also related to U.S. patent application Ser. No. 12/798,324 entitled “OCULAR SURFACE INTERFEROMETRY (OSI) DEVICES AND SYSTEMS FOR IMAGING AND MEASURING OCULAR TEAR FILM LAYER THICKNESS(ES),” filed on Apr. 1, 2010, issued as U.S. Pat. No. 8,215,774, which is incorporated herein by reference in its entirety.

The present application is being filed with three (3) sets of color versions of the drawings discussed and referenced in this disclosure. Color drawings more fully disclose the subject matter disclosed herein.

FIELD OF THE DISCLOSURE

The technology of the disclosure relates to imaging a mammalian ocular tear film. The technology of the disclosure also relates to measuring ocular tear film layer thickness(es), including lipid layer thickness (LLT) and/or aqueous layer thickness (ALT). Imaging the ocular tear film and measuring TFLT may be used to diagnose “dry eye,” which may be due to any number of deficiencies, including lipid deficiency and aqueous deficiency.

BACKGROUND

In the human eye, the precorneal tear film covering ocular surfaces is composed of three primary layers: the mucin layer, the aqueous layer, and the lipid layer. Each layer plays a role in the protection and lubrication of the eye and thus affects dryness of the eye or lack thereof. Dryness of the eye is a recognized ocular disease, which is generally referred to as “dry eye,” “dry eye syndrome” (DES), or “keratoconjunctivitis sicca” (KCS). Dry eye can cause symptoms, such as itchiness, burning, and irritation, which can result in discomfort. There is a correlation between the ocular tear film layer thicknesses and dry eye disease. The various different medical conditions and damage to the eye as well as the relationship of the aqueous and lipid layers to those conditions are reviewed in Surv Opthalmol 52:369-374, 2007 and additionally briefly discussed below.

As illustrated in FIG. 1, the precorneal tear film includes an innermost layer of the tear film in contact with a cornea 10 of an eye 11 known as the mucus layer 12. The mucus layer 12 is comprised of many mucins. The mucins serve to retain aqueous in the middle layer of the tear film known as the aqueous layer. Thus, the mucus layer 12 is important in that it assists in the retention of aqueous on the cornea 10 to provide a protective layer and lubrication, which prevents dryness of the eye 11.

A middle or aqueous layer 14 comprises the bulk of the tear film. The aqueous layer 14 is formed by secretion of aqueous by lacrimal glands 16 and accessory tear glands 17 surrounding the eye 11, as illustrated in FIG. 2. The aqueous, secreted by the lacrimal glands 16 and accessory tear glands 17, is also commonly referred to as “tears.” One function of the aqueous layer 14 is to help flush out any dust, debris, or foreign objects that may get into the eye 11. Another important function of the aqueous layer 14 is to provide a protective layer and lubrication to the eye 11 to keep it moist and comfortable. Defects that cause a lack of sufficient aqueous in the aqueous layer 14, also known as “aqueous deficiency,” are a common cause of dry eye. Contact lens wear can also contribute to dry eye. A contact lens can disrupt the natural tear film and can reduce corneal sensitivity over time, which can cause a reduction in tear production.

The outermost layer of the tear film, known as the “lipid layer” 18 and also illustrated in FIG. 1, also aids to prevent dryness of the eye. The lipid layer 18 is comprised of many lipids known as “meibum” or “sebum” that is produced by meibomian glands 20 in upper and lower eyelids 22, 24, as illustrated in FIG. 3. This outermost lipid layer is very thin, typically less than 250 nanometers (nm) in thickness. The lipid layer 18 provides a protective coating over the aqueous layer 14 to limit the rate at which the aqueous layer 14 evaporates. Blinking causes the upper eyelid 22 to mall up aqueous and lipids as a tear film, thus forming a protective coating over the eye 11. A higher rate of evaporation of the aqueous layer 14 can cause dryness of the eye. Thus, if the lipid layer 18 is not sufficient to limit the rate of evaporation of the aqueous layer 14, dryness of the eye may result.

Notwithstanding the foregoing, it has been a long standing and vexing problem for clinicians and scientists to quantify the lipid and aqueous layers and any deficiencies of same to diagnose evaporative tear loss and/or tear deficiency dry eye conditions. Further, many promising treatments for dry eye have failed to receive approval from the United States Food and Drug Administration due to the inability to demonstrate clinical effectiveness to the satisfaction of the agency. Many clinicians diagnose dry eye based on patient symptoms alone. Questionnaires have been used in this regard. Although it seems reasonable to diagnose dry eye based on symptoms alone, symptoms of ocular discomfort represent only one aspect of “dry eyes,” as defined by the National Eye Institute workshop on dry eyes. In the absence of a demonstrable diagnosis of tear deficiency or a possibility of excessive tear evaporation and damage to the exposed surface of the eye, one cannot really satisfy the requirements of dry eye diagnosis.

SUMMARY OF THE DETAILED DESCRIPTION

Embodiments of the detailed description include background reduction apparatuses and methods of ocular surface interferometry (OSI) employing polarization for imaging an ocular tear film and/or measuring a tear film layer thickness (TFLT) of a mammalian's ocular tear film. The background reduction apparatuses and methods of OSI employing polarization can be used to measure the thickness of the lipid layer component (LLT) and/or the aqueous layer component (ALT) of the ocular tear film. “TFLT” as used herein includes LLT, ALT, or both LLT and ALT. “Measuring TFLT” as used herein includes measuring LLT, ALT, or both LLT and ALT. Imaging the ocular tear film and measuring TFLT can be used in the diagnosis of the tear film, including but not limited to lipid layer and aqueous layer deficiencies. These characteristics may be the cause or contributing factor to a patient experiencing dry eye syndrome (DES).

In this regard, embodiments disclosed herein include a multi-wavelength light source that is controlled to direct light in the visible region to an ocular tear film. The light source may be a Lambertian emitter that provides a uniform or substantially uniform intensity in all directions of emission. The light source is arranged such that light rays emitted from the light source are specularly reflected from the tear film and undergo constructive and destructive optical wave interference interactions (also referred to as “interference interactions”) in the ocular tear film. An imaging device having a detection spectrum that includes the spectrum of the light source is focused on an area(s) of interest on the lipid layer of the tear film. The imaging device captures the interference interactions (i.e., modulation) of specularly reflected light rays from the illuminated tear film coming together by the focusing action of the imaging device in an image. The imaging device then captures the optical wave interference signals (also referred to as “interference signals”) representing the interference interactions of specularly reflected light from the tear film. The imaging device produces an output signal(s) representative of the interference signal in an image. The image may contain an interference signal for a given imaged pixel or pixels of the lipid layer by the imaging device.

The image can be displayed to a technician or other user. The image can also be processed and analyzed to measure a TFLT in the area or region of interest of the ocular tear film. In one embodiment, a background signal(s) that does not represent specularly reflected light from the tear film which is superimposed on the interference signal(s) is reduced by polarization. This is referred to as “background reduction” in the present disclosure. The background signal(s) includes returned captured light that is not specularly reflected from the tear film and thus does not contain optical wave interference information (also referred to as “interference information”). For example, the background signal(s) may include stray, ambient light entering into the imaging device, scattered light from the patient's face and eye structures outside and within the tear film as a result of ambient light and diffuse illumination by the light source, and eye structure beneath the tear film, and particularly contribution from the extended area of the source itself. The background signal(s) adds a bias (i.e., offset) error to the interference signal(s) thereby reducing interference signal strength and contrast. This error can adversely influence measurement of TFLT. Further, if the background signal(s) has a color hue different from the light of the light source, a color shift can also occur to the captured optical wave interference (also referred to as “interference”) of specularly reflected light thus introducing further error.

In this regard, the apparatus for imaging the ocular tear film is disclosed that is configured to capture an image that includes interference interactions of specularly reflecting light from the tear film and reduce the intensity of the background offset superimposed on the image. The captured image can then be displayed on a visual display to be analyzed by a technician and/or processed and analyzed to measure a TFLT. The apparatus for imaging the ocular tear film comprises a multi-wavelength light source configured to direct a multi-wavelength light including unpolarized light having a first intensity in an illumination path to illuminate a region of interest (ROI) of an ocular tear film. While the ROI of the ocular tear film is illuminated, a specularly reflected light is produced in a first polarization plane containing optical wave interference. A polarizer is disposed in the illumination path. The polarizer has a polarization axis that is parallel or substantially parallel to the first polarization plane of the specularly reflected light. As such, a background signal comprised of unpolarized light is returned from the ROI of the ocular tear film to have a second intensity less than the first intensity. An imaging device is configured to capture the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film. A control system is configured to receive at least one image containing the optical wave interference of specularly reflected light and the background signal captured by the imaging device while illuminated by multi-wavelength light passing through the polarizer. One non-limiting benefit of the apparatus is that the image of the ROI of the ocular tear film is captured with a significantly reduced background signal due to the polarization of the unpolarized light that typically makes up the background signal. Therefore, computationally intense processing that might otherwise be necessary to digitally reduce or remove the background signal from the at least one image is avoided.

In another embodiment, a method of imaging an ocular tear film is disclosed. The disclosed method involves directing multi-wavelength light including unpolarized light having a first intensity in an illumination path to illuminate the ROI of the ocular tear film. A specularly reflected light is produced in a first polarization plane containing optical wave interference while ROI of the ocular tear film is being illuminated. The method also includes polarizing the unpolarized light to cause the background signal comprised of unpolarized light returned from the ROI of the ocular tear film to have a second intensity that is less than the first intensity. The method also includes capturing at least one image of the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film. The method further includes receiving the at least one image containing the optical wave interference of specularly reflected light and the background signal, which is significantly reduced due to the polarization of the unpolarized light that typically makes up the background signal. One non-limiting benefit of the method is that computationally intense processing that might otherwise be necessary to digitally reduce or remove the background signal from the at least one image is avoided.

After the interference of the specularly reflected light is captured in an image, the interference signal is produced from any method or device disclosed in this disclosure, the captured image can also be pre-processed before being processed and analyzed to measure TFLT. Pre-processing can involve performing a variety of methods to improve the quality of the resulting interference signal, including but not limited to detecting and removing eye blinks or other signals in the captured images that hinder or are not related to the tear film. After pre-processing, the interference signal or representations thereof can be processed to be compared against a tear film layer interference model to measure TFLT. The interference signal can be processed and converted by the imaging device into digital red-green-blue (RGB) component values which can be compared to RGB component values in a tear film interference model to measure TFLT on an image pixel-by-pixel basis. The tear film interference model is based on modeling the lipid layer of the tear film in various thicknesses and mathematically or empirically observing and recording resulting interference interactions of specularly reflected light from the tear film model when illuminated by the light source and detected by a camera (imaging device).

In a tear film interference model, the lipid layer is modeled of various LLTs to observe interference interactions resulting from the various LLTs. The aqueous layer may be modeled in the tear film interference model to be of an infinite, minimum, or varying thickness. If the aqueous layer is modeled to be of an infinite thickness, the tear film interference model assumes no specular reflections occur from the aqueous-to-mucin layer transition. If the aqueous layer is modeled to be of a certain minimum thickness (˜>2 μm e.g.), the effect of specular reflection from the aqueous-to-mucin layer transition may be considered in the resulting interference. In either case, the tear film interference model is a 2-wave tear film interference model to represent the interference between specularly reflected light from the air-to lipid layer transition and the lipid-to-aqueous layer transition. Thus, a 2-wave tear film interference model will include one-dimension of data comprised of interference interactions corresponding to the various LLTs. In this case, to measure LLT the interference interactions in the interference signal representing specularly reflected light from the tear film produced by the imaging device are compared to the interference patterns in the tear film interference model. However, if the aqueous layer is also modeled to be of varying ALTs, the tear film interference model will be a 3-wave tear film interference model. The 3-wave tear film interference model will include interference between the air-to lipid layer, lipid-to-aqueous layer, and aqueous-to-mucus/cornea layer transitions. As a result, a 3-wave tear film interference model will include two-dimensions of data comprised of interference interactions corresponding to various LLT and ALT combinations. In this case, to measure LLT and/or ALT the interference interactions from the interference signal representing specularly reflected light from the tear film produced by the imaging device can be compared to interference interactions in the 3-wave tear film interference model.

The tear film interference model can be a theoretical tear film interference model where the light source and the tear film layers are modeled mathematically. The tear film layers may be mathematically modeled by modeling the tear film layers after certain biological materials. Interference interactions from the mathematically modeled light source illuminating the mathematically modeled tear film and received by the mathematically modeled camera are calculated and recorded for varying TFLTs. Alternatively, the tear film interference model can be based on a biological or phantom tear film model comprised of biological or phantom tear film layers. The actual light source is used to illuminate the biological or phantom tear film model and interference interactions representing interference of specularly reflected light are empirically observed and recorded for various TFLTs using the actual camera.

Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention.

FIG. 1 is a side view of an exemplary eye showing the three layers of the tear film in exaggerated form;

FIG. 2 is a front view of an exemplary eye showing the lacrimal and accessory tear glands that produce aqueous in the eye;

FIG. 3 illustrates exemplary upper and lower eyelids showing the meibomian glands contained therein;

FIGS. 4A-4H illustrate relationships between light waves, beam splitters, and polarizers;

FIG. 5 illustrates a general principle of operation for embodiments of the present disclosure;

FIGS. 6A and 6B illustrate of an exemplary light source and imaging device to facilitate discussion of illumination of the tear film and capture of interference interactions of specularly reflected light from the tear film;

FIG. 7 illustrates (in a microscopic section view) exemplary tear film layers to illustrate how light rays can specularly reflect from various tear film layer transitions;

FIG. 8 is a flowchart of an exemplary process for obtaining one or more interference signals from images of a tear film representing specularly reflected light from the tear film with the background signal reduced or substantially reduced;

FIG. 9 illustrates an exemplary image focused on a lipid layer of a tear film and capturing interference interactions of specularly reflected light from an area or region of interest of the tear film;

FIG. 10A is a side view of an embodiment of an exemplary OSI device that in accordance with the present disclosure includes a second polarizer;

FIG. 10B is a top view of the embodiment of the OSI device shown in FIG. 10A;

FIG. 11 illustrates an exemplary image captured while utilizing both the first polarizer in an illumination path and a second polarizer in an imaging path;

FIG. 12 is a perspective view of an exemplary ocular surface interferometry (OSI) device for illuminating and imaging a patient's tear film, displaying images, analyzing the patient's tear film, and generating results from the analysis of the ocular tear film;

FIG. 13 is a side view of the OSI device of FIG. 12 illuminating and imaging an eye and tear film;

FIGS. 14A and 14B depict the OSI device configured to include an exemplary rotatable holder that holds the second polarizer;

FIG. 15 is a top view of an illumination device provided in the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A and 14B illuminating an ocular tear film with the video camera capturing images of the patient's tear film;

FIG. 16 is a perspective view of an exemplary printed circuit board (PCB) with a plurality of light emitting diodes (LED) provided in the illumination device of the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A and 14B to illuminate the ocular tear film;

FIG. 17 is a perspective view of the illumination device and housing in the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A and 14B;

FIG. 18A illustrates an exemplary system diagram of a control system and supporting components that can include the exemplary OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 18B is a flowchart illustrating an exemplary overall processing that can be employed by of the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B having systems components according to the exemplary system diagram of the OSI device in FIG. 18A;

FIG. 19 is a flowchart illustrating exemplary pre-processing steps performed on the images of an ocular tear film before measuring tear film layer thickness (TFLT);

FIG. 20 is an exemplary graphical user interface (GUI) for controlling imaging, pre-processing, and post-processing settings that can be employed by the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 21 is an exemplary tear film image taken with a VGA (640×480) video camera having a 25 mm fixed focal length lens.

FIGS. 22A and 22B illustrate exemplary threshold masks that may be used to provide a threshold function during pre-processing of a resulting image containing specularly reflected light from a patient's tear film;

FIG. 23 illustrates an exemplary image of FIG. 21 after a threshold pre-processing function has been performed leaving interference of the specularly reflected light from the patient's tear film;

FIG. 24 illustrates an exemplary image of the image of FIG. 23 after erode and dilate pre-processing functions have been performed on the image;

FIG. 25 illustrates an exemplary histogram used to detect eye blinks and/or eye movements in captured images or frames of a tear film;

FIG. 26 illustrates an exemplary process for loading an International Colour Consortium (ICC) profile and tear film interference model into the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 27 illustrates a flowchart providing an exemplary visualization system process for displaying images of a patient's tear film on a display in the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 28 illustrates an example of a tear film image that is displayed on the display 174 of the OSI device 170.

FIG. 29 illustrates an exemplary post-processing system that may be provided in the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 30A illustrates an exemplary 3-wave tear film interference model based on a 3-wave theoretical tear film model to correlate different observed interference color with different lipid layer thicknesses (LLTs) and aqueous layer thicknesses (ALTs);

FIG. 30B illustrates another exemplary 3-wave tear film interference model based on a 3-wave theoretical tear film model to correlate different observed interference color with different lipid layer thicknesses (LLTs) and aqueous layer thicknesses (ALTs);

FIG. 31 is another representation of the 3-wave tear film interference model of FIGS. 30A and 30B with normalization applied to each red-green-blue (RGB) color value individually;

FIG. 32 is an exemplary histogram illustrating results of a comparison of interference interactions from the interference signal of specularly reflected light from an occular tear film to the 3-wave tear film interference model of FIGS. 30A-31 for measuring TFLT of a patient's tear film;

FIG. 33 is an exemplary histogram plot of distances in pixels between RGB color value representation of interference interactions from the interference signal of specularly reflected light from an ocular tear film and the nearest distance RGB color value in the 3-wave tear film interference model of FIGS. 30A-31;

FIG. 34 is an exemplary threshold mask used during pre-processing of the tear film images;

FIG. 35 is an exemplary three-dimensional (3D) surface plot of the measured LLT and ALT thicknesses of a patient's tear film;

FIG. 36 is an exemplary image representing interference interactions of specularly reflected light from an ocular tear film results window based on replacing a pixel in the tear film image with the closest matching RGB color value in the normalized 3-wave tear film interference model of FIG. 31;

FIG. 37 is an exemplary TFLT palette curve for a TFLT palette of LLTs plotted in RGB space for a given ALT in three-dimensional (3D) space;

FIG. 38 is an exemplary TFLT palette curve for the TFLT palette of FIG. 37 with LLTs limited to a maximum LLT of 240 nm plotted in RGB space for a given ALT in three-dimensional (3D) space;

FIG. 39 illustrates the TFLT palette curve of FIG. 38 with an acceptable distance to palette (ADP) filter shown to determine tear film pixel values having RGB values that correspond to ambiguous LLTs;

FIG. 40 is an exemplary login screen to a user interface system for controlling and accessing the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 41 illustrates an exemplary interface screen for accessing a patient database interface in the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 42 illustrates a patient action control box for selecting to either capture new tear film images of a patient in the patient database or view past captured images of the patient from the OSI devices of FIGS. 6A, 6B, 10A, 10B, 12, 13, 14A, and 14B;

FIG. 43 illustrates a viewing interface for viewing an ocular tear film either captured in real-time or previously captured by the OSI devices of FIGS. 12 and 13;

FIG. 44 illustrates a tear film image database for a patient;

FIG. 45 illustrates a view images GUI screen showing an overlaid image of interference interactions of the interference signals from specularly reflected light from a patient's tear film overtop an image of the patient's eye for both the patient's left and right eyes side by side; and

FIG. 46 illustrates the GUI screen of FIG. 45 with the images of the patient's eye toggled to show only the interference interactions of the interference signals from specularly reflected light from a patient's tear film.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

Embodiments of the detailed description include background reduction apparatuses and methods of ocular surface interferometry (OSI) employing polarization for imaging an ocular tear film and/or measuring a tear film layer thickness (TFLT) of a mammalian's ocular tear film. The background reduction apparatuses and methods of OSI employing polarization can be used to measure the thickness of the lipid layer component (LLT) and/or the aqueous layer component (ALT) of the ocular tear film. “TFLT” as used herein includes LLT, ALT, or both LLT and ALT. “Measuring TFLT” as used herein includes measuring LLT, ALT, or both LLT and ALT. Imaging the ocular tear film and measuring TFLT can be used in the diagnosis of the tear film, including but not limited to lipid layer and aqueous layer deficiencies. These characteristics may be the cause or contributing factor to a patient experiencing dry eye syndrome (DES).

In this regard, embodiments disclosed herein include a multi-wavelength light source that is controlled to direct light in the visible region to an ocular tear film. The light source may be a Lambertian emitter that provides a uniform or substantially uniform intensity in all directions of emission. The light source is arranged such that light rays emitted from the light source are specularly reflected from the tear film and undergo constructive and destructive optical wave interference interactions (also referred to as “interference interactions”) in the ocular tear film. An imaging device having a detection spectrum that includes the spectrum of the light source is focused on an area(s) of interest on the lipid layer of the tear film. The imaging device captures the interference interactions (i.e., modulation) of specularly reflected light rays from the illuminated tear film coming together by the focusing action of the imaging device in an image. The imaging device then captures the optical wave interference signals (also referred to as “interference signals”) representing the interference interactions of specularly reflected light from the tear film. The imaging device produces an output signal(s) representative of the interference signal in an image. The image may contain an interference signal for a given imaged pixel or pixels of the lipid layer by the imaging device.

The image can be displayed to a technician or other user. The image can also be processed and analyzed to measure a TFLT in the area or region of interest of the ocular tear film. In one embodiment, a background signal(s) that does not represent specularly reflected light from the tear film which is superimposed on the interference signal(s) is reduced by polarization. This is referred to as “background reduction” in the present disclosure. The background signal(s) includes returned captured light that is not specularly reflected from the tear film and thus does not contain optical wave interference information (also referred to as “interference information”). For example, the background signal(s) may include stray, ambient light entering into the imaging device, scattered light from the patient's face and eye structures outside and within the tear film as a result of ambient light and diffuse illumination by the light source, and eye structure beneath the tear film, and particularly contribution from the extended area of the source itself. The background signal(s) adds a bias (i.e., offset) error to the interference signal(s) thereby reducing interference signal strength and contrast. This error can adversely influence measurement of TFLT. Further, if the background signal(s) has a color hue different from the light of the light source, a color shift can also occur to the captured optical wave interference (also referred to as “interference”) of specularly reflected light thus introducing further error.

In this regard, the apparatus for imaging the ocular tear film is disclosed that is configured to capture an image that includes interference interactions of specularly reflecting light from the tear film and reduce the intensity of the background offset superimposed on the image. The captured image can then be displayed on a visual display to be analyzed by a technician and/or processed and analyzed to measure a TFLT. The apparatus for imaging the ocular tear film comprises a multi-wavelength light source configured to direct a multi-wavelength light including unpolarized light having a first intensity in an illumination path to illuminate a region of interest (ROI) of an ocular tear film. While the ROI of the ocular tear film is illuminated, a specularly reflected light is produced in a first polarization plane containing optical wave interference. A polarizer is disposed in the illumination path. The polarizer has a polarization axis that is parallel or substantially parallel to the first polarization plane of the specularly reflected light. As such, a background signal comprised of unpolarized light is returned from the ROI of the ocular tear film to have a second intensity less than the first intensity. An imaging device is configured to capture the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film. A control system is configured to receive at least one image containing the optical wave interference of specularly reflected light and the background signal captured by the imaging device while illuminated by multi-wavelength light passing through the polarizer. One non-limiting benefit of the apparatus is that the image of the ROI of the ocular tear film is captured with a significantly reduced background signal due to the polarization of the unpolarized light that typically makes up the background signal. Therefore, computationally intense processing that might otherwise be necessary to digitally reduce or remove the background signal from the at least one image is avoided.

Before discussing the particular embodiments of the present disclosure, a discussion of the electromagnetic nature of light waves is provided with regard to FIGS. 4A-4H. Light waves, like all electromagnetic waves, propagate with an oscillating electric field that generates an oscillating magnetic field that regenerates the oscillating electric field and so on. Moreover, light waves exhibit a property known as polarization. For example, when the orientation of the oscillating electric field is in a fixed plane in space, the light wave is a plane-polarized wave. When the plane of the electric field rotates as a light wave propagates spirally through space, the light wave is a circularly or elliptically polarized light wave. Furthermore, light made up of many light waves that are randomly polarized is referred to as unpolarized light, since there is no single polarization plane for unpolarized light.

Optical filters known as polarizers allow unimpeded transmission of light waves having a single polarization-plane. Any type of polarizer may be employed in the embodiments discussed below. For example, a linear polarizer may be employed to reduce the intensity of a background(s) signal. An exemplary linear polarizer has a polarization axis that typically extends across the polarizer. Light waves that impinge upon the linear polarizer with a polarization-plane that is parallel to the polarization axis of the linear polarizer will pass through the linear polarizer unimpeded. In contrast, light waves that impinge upon the linear polarizer with polarization-planes that are not parallel to the polarization of the linear polarizer will be impeded. As another non-limiting example, a circular polarizer or an elliptical polarizer can be employed in any of the embodiments below to reduce the intensity of a background signal(s). Circular polarizers and/or elliptical polarizers may also be usable to prevent unintentional secondary specular reflections in embodiments that use beam splitters. An exemplary circular polarizer may comprise two components. One component is a linear polarizer such as the exemplary polarizer described above that passes light waves in one polarization-plane. The other component is a quarter wave plate that transforms light waves passing through the linear polarizer in one polarization-plane into circularly polarized light waves. Exemplary elliptical polarizers may comprise the same components as circular polarizers. An elliptical polarizer is configured such that it transforms the light passing through the linear polarizer in one polarization-plane into elliptically polarized light. Elliptically polarized light has unequal electric field amplitudes.

The intensity of a light wave is related to its electric field amplitude. The degree to which the intensity of a light wave is reduced by a polarizer depends on the angle between the polarization plane of the light wave and the polarization axis of the polarizer. According to Malus' law, a light wave impinging on a polarizer will be reduced in amplitude in proportion to the cosine of the angle between the polarization plane of the light wave and the polarization axis of the polarizer. A light wave that has a polarization plane that is parallel with the polarization axis will have a 0° angle between its polarization plane and the polarization axis of the polarizer. Since the cosine of 0° is one, Malus' law ideally predicts no reduction of light intensity for a light wave that has a polarization plane that is parallel with the polarization axis. In contrast, Malus' law ideally predicts no transmission through a polarizer for a light wave that impinges on the polarizer with a polarization plane that is perpendicular to the polarization axis of the polarizer since the cosine of 90° is zero.

When unpolarized light impinges on a polarizer, the overall intensity of the light is reduced by at least 50% due to the summations of amplitude reductions due to Malus' law as applied to individual light waves having random polarization planes impinging on the polarizer. Light that is transmitted through the polarizer becomes polarized such that the light has a polarization plane that is parallel with the polarization axis of the polarizer.

Light intensity is proportional to the square of the amplitude. Therefore, the intensity of light transmitted through the polarizer from a non-polarized light source is ideally 25%. However, modern polarizers are not perfect, which results in additional losses of intensity for the transmitted light due to absorption, scattering and other intensity degrading effects.

In this regard, FIGS. 4A through 4H illustrate relationships between light waves, polarizers, and beam splitters. Referring to FIG. 4A, a polarizer 30 has a polarization axis 32 that is oriented in a direction indicated by a polarization axis arrow. A light wave 34 impinging on the polarizer 30 is in a polarization plane that is parallel to the polarization axis 32 of the polarizer 30. As a result, the light wave 34 is transmitted unimpeded through the polarizer 30.

In contrast, FIG. 4B shows the polarizer 30 rotated such that the polarization axis 32 is perpendicular to the polarization plane of the light wave 34 as indicated by the polarization axis arrow. In this case, none of the light wave 34 will be transmitted through the polarizer 30. FIG. 4C and FIG. 4D represent the same conditions as FIG. 4A and FIG. 4B respectively. However, the polarization plane of light wave 34 is represented by double-headed arrows 36 instead of the sine wave representation used to represent light wave 34 in FIGS. 4A and 4B.

FIG. 4E illustrates a condition wherein the light wave 34 impinges upon the polarizer 30 when the difference in the angle between the polarization plane of the light wave 34 and the polarization axis 32 is intermediate of parallel and perpendicular. In this case, a portion of the light wave 34 is transmitted through the polarizer 30. The portion of light wave 34 that is transmitted through the polarizer 30 obtains a polarization plane that is parallel to the polarization axis 32 of the polarizer 30. The intensity of the transmitted portion of the light wave 34 is reduced relative to the intensity of the light wave 34 that is impinging on the polarizer 30. The relative intensity of the light wave 34 is represented by the relative difference in length of the double-headed arrows 36.

FIG. 4F illustrates a light beam 38 that is shown impinging on the polarizer 30. The light beam 38 is made up of a plurality of light waves that are in random polarization planes. In this example, the light beam 38 includes the light wave 34 having a polarization plane that aligns with the polarization axis 32 of the polarizer 30. As a result of the alignment, the light wave 34 is transmitted through the polarizer 30.

FIG. 4G illustrates a specular reflection and a refraction of the light wave 34 as the light wave 34 impinges on the minor-like surface of a beam splitter 40. In the example of FIG. 4G, the light wave 34 has a first polarization plane as it arrives at beam splitter 40. A first portion 42 of the light wave 34 specularly reflects from the beam splitter 40 in a second polarization plane that is perpendicular to the first polarization plane of the impinging light wave 34. A second portion 44 of the light wave 34 is refracted by the beam splitter 40. The second portion 44 of the light wave 34 maintains the first polarization plane of the impinging light wave 34.

FIG. 4H illustrates a specular reflection and a refraction of the light wave 34 that is one of a plurality of light waves that make up the light beam 38 as it impinges upon the beam splitter 40. As in the previous case, the light wave 34 in the first polarization plane is split into the first portion 42 and the second portion 44. As before, the first portion 42 of the light wave 34 is specularly reflected from the beam splitter 40 in a polarization plane that is perpendicular to the first polarization plane of the impinging light wave 34. As before, the second portion 44 of the light wave 34 maintains the first polarization plane of the impinging light wave 34.

FIG. 5 illustrates exemplary devices that can be provided in an OSI device according to a first embodiment. An optical system 46 is made up of a light source 48, a beam splitter 50, a first polarizer 52 having a polarization axis 54 and a second polarizer 56 having a polarization axis 58. In the exemplary case of FIG. 5, light 60 emitted from the light source 48 is unpolarized. However, the exemplary case of FIG. 5 should not be viewed as limiting the present disclosure to unpolarized illumination. The unpolarized light is directed from the light source 48 to a target 62. The target 62 reflects the unpolarized light to the beam splitter 50. A portion of the unpolarized light reflects from the beam splitter 50 to the first polarizer 52. A portion of the unpolarized light 60 having a polarization plane that aligns with the polarization axis 54 passes through the first polarizer 52 unimpeded. A summation of other light waves making up the unpolarized light 60 having polarization planes that are not perpendicular to the polarization axis 54 are also transmitted through the first polarizer 52 with reduced intensity. Light waves 64 that are transmitted through the first polarizer 52 each have a polarization plane that is parallel to the polarization axis 54.

A refracted portion of the unpolarized light 60 is directed to the second polarizer 56. Similar to the light interaction with the first polarizer 52, a portion of the unpolarized light 60 having a polarization plane that aligns with the polarization axis 58 passes through the second polarizer 56 unimpeded. A summation of other light waves making up the unpolarized light 60 having polarization planes that are not perpendicular to the polarization axis 58 are also transmitted through the second polarizer 56 with reduced intensity. Light waves 66 that are transmitted through the second polarizer 56 each have a polarization plane that is parallel to the polarization axis 58.

Another portion of the unpolarized light 60 emitted from the light source 48 is specularly reflected from the target 62 such that a polarized light 68 is directed to the beam splitter 50. A first portion of the polarized light 68 is specularly reflected from the beam splitter 50 so that the polarized light is re-polarized in a polarization plane that is perpendicular to the polarization axis 54 of the first polarizer 52. In this manner, the polarized light 68 that is specularly reflected from the target 62 is practically prevented from passing through the first polarizer 52. In contrast, a portion of the polarized light 68 that is refracted through the beam splitter 50 retains the polarization plane of the polarized light 68 as it specularly reflects from the target 62. The polarization axis 58 of the second polarizer 56 is aligned such that the first portion of the polarized light 68 specularly reflected from the target 62 passes through the second polarizer 56 unimpeded.

Against the discussion above, embodiments of disclosed herein and discussed in more detail below include ocular surface interferometry (OSI) devices, systems, and methods for measuring a tear film layer thickness (TFLT) in a patient's ocular tear film. The OSI devices, systems, and methods can be used to measure the thickness of the lipid layer component (LLT) and/or the aqueous layer component (ALT) of the ocular tear film. “TFLT” as used herein includes LLT, ALT, or both LLT and ALT. “Measuring TFLT” as used herein includes measuring LLT, ALT, or both LLT and ALT. Measuring TFLT can be used in the diagnosis of a patient's tear film, including but not limited to lipid layer and aqueous layer deficiencies. These characteristics may be the cause or contributing factor to a patient experiencing dry eye syndrome (DES).

In this regard, embodiments disclosed herein include a light source that is controlled to direct light in the visible region to an ocular tear film. For example, the light source may be a Lambertian emitter that provides a uniform or substantially uniform intensity in all directions of emission. The light source is arranged such that light rays emitted from the light source are specularly reflected toward an imaging device from the tear film and undergo constructive and destructive interference interactions in the ocular tear film. An imaging device having a detection spectrum that includes the spectrum of the light source is focused on an area(s) of interest on the lipid layer of the tear film. The imaging device captures a image of the interference interactions (i.e., modulation) of specularly reflected light rays from the illuminated tear film coming together by the focusing action of the imaging device. The imaging device then captures the interference signals representing the interference interactions of specularly reflected light from the tear film. The imaging device produces an output signal(s) representative of the interference signal in a image. The image may contain an interference signal for a given imaged pixel or pixels of the lipid layer by the imaging device. The output signal(s) can be processed and analyzed to measure a TFLT in the area or region of interest of the ocular tear film.

OSI Device with Polarizer in Illumination Path

In this regard, FIGS. 6A and 6B illustrate a general embodiment of an ocular surface interferometry (OSI) device 70. Other embodiments will be described later in this application. In general, the OSI device 70 is configured to illuminate a patient's ocular tear film, capture images of interference interactions of specularly reflected light from the ocular tear film, and process and analyze the interference interactions to measure TFLT. As shown in FIG. 6A, the exemplary OSI device 70 positioned in front of one of the patient's eye 72 is shown from a side view. A top view of the patient 74 in front of the OSI device 70 is illustrated in FIG. 6B. The ocular tear film of a patient's eyes 72 is illuminated with a light source 76 (also referred to herein as “illuminator 76”) and comprises a large area light source having a spectrum in the visible region adequate for TLFT measurement and correlation to dry eye. The illuminator 76 can be a white or multi-wavelength light source.

In this embodiment, the illuminator 76 is a Lambertian emitter and is adapted to be positioned in front of the eye 72 on a stand 78. As employed herein, the terms “Lambertian surface” and “Lambertian emitter” are defined to be a light emitter having equal or substantially equal (also referred to as “uniform” or substantially uniform) intensity in all directions. This allows the imaging of a uniformly or substantially uniformly bright tear film region for TFLT, as discussed in more detail in this disclosure. The illuminator 76 comprises a large surface area emitter, arranged such that rays emitted from the emitter are specularly reflected from the ocular tear film and undergo constructive and destructive interference in tear film layers therein. A polarizer 86 polarizes light emitted from the illuminator 76. The polarizer 86 has a polarization axis 88 that is aligned parallel or substantially parallel to the polarization plane of the specularly reflected light from patient's 74 ocular tear film. An image of the patient's 74 lipid layer is the backdrop over which the interference image is seen and it should be as spatially uniform as possible.

An imaging device 80 is included in the OSI device 70 and is employed to capture interference interactions of specularly reflected light from the patient's 74 ocular tear film when illuminated by the illuminator 76. The imaging device 80 may be a still or video camera, or other device that captures images and produces an output signal representing information in captured images. The output signal may be a digital representation of the captured images. The geometry of the illuminator 76 can be understood by starting from an imaging lens 82 of the imaging device 80 and proceeding forward to the eye 72 and then to the illuminator 76. The fundamental equation for tracing ray lines is Snell's law, which provides:

n1 Sin Θ₁ =n2 Sin Θ₂,

where “n1” and “n2” are the indexes of refraction of two mediums containing the ray, and θ₁ and θ₂ is the angle of the ray relative to the normal from the transition surface. As illustrated in FIG. 7, light rays 100 are directed by the illuminator 76 to an ocular tear film 102. In the case of specularly reflected light 104 that does not enter a lipid layer 106 and instead reflects from an anterior surface 108 of the lipid layer 106, Snell's law reduces down to Θ₁=Θ₂, since the index of refraction does not change (i.e., air in both instances). Under these conditions, Snell's law reduces to the classical law of reflection such that the angle of incidence is equal and opposite to the angle of reflectance. Some of the light rays 110 pass through the anterior surface 108 of the lipid layer 106 and enter into the lipid layer 106, as illustrated in FIG. 7. As a result, the angle of these light rays 110 (i.e., Θ₃) normal to the anterior surface 108 of the lipid layer 106 will be different than the angle of the light rays 100 (Θ₁) according to Snell's law. This is because the index of refraction of the lipid layer 106 is different than the index of refraction of air. Some of the light rays 110 passing through the lipid layer 106 will specularly reflect from the lipid layer-to-aqueous layer transition 112 thereby producing specularly reflected light rays 114. The specularly reflected light rays 104, 114 undergo constructive and destructive interference anterior of the lipid layer 106. The modulations of the interference of the specularly reflected light rays 104, 114 superimposed on the anterior surface 108 of the lipid layer 106 are collected by the imaging device 80 when focused on the anterior surface 108 of the lipid layer 106. Focusing the imaging device 80 on the anterior surface 108 of the lipid layer 106 allows capturing of the modulated interference information at the plane of the anterior surface 108. In this manner, the captured interference information and the resulting calculated TFLT from the interference information is spatially registered to a particular area of the tear film 102 since that the calculated TFLT can be associated with such particular area, if desired.

The thickness of the lipid layer 106 (‘d₁’) is a function of the interference interactions between specularly reflected light rays 104, 114. The thickness of the lipid layer 106 (‘d₁’) is on the scale of the temporal (or longitudinal) coherence of the light source 76. Therefore, thin lipid layer films on the scale of one wavelength of visible light emitted by the light source 76 offer detectable colors from the interference of specularly reflected light when viewed by a camera or human eye. The colors may be detectable as a result of calculations performed on the interference signal and represented as a digital values including but not limited to a red-green-blue (RGB) value in the RGB color space. Quantification of the interference of the specularly reflected light can be used to measure LLT. The thicknesses of an aqueous layer 116 (‘d₂’) can also be determined using the same principle. Some of the light rays 110 (not shown) passing through the lipid layer 106 can also pass through the lipid-to-aqueous layer transition 112 and enter into the aqueous layer 116 specularly reflecting from the aqueous-to-mucin/cornea layer transition 118. These specular reflections also undergo interference with the specularly reflected light rays 104, 114. The magnitude of the reflections from each interface depends on the refractive indices of the materials as well as the angle of incidence, according to Fresnel's equations, and so the depth of the modulation of the interference interactions is dependent on these parameters, thus so is the resulting color.

Turning back to FIGS. 6A and 6B, the illuminator 76 in this embodiment is a broad spectrum light source covering the visible region between about 400 nm to about 700 nm. The illuminator 76 contains an arced or curved housing 90 (see FIG. 6B) into which individual light emitters are mounted, subtending an arc of approximately 130 degrees from the optical axis of the eye 72 (see FIG. 6B). A curved surface may present better uniformity and be more efficient, as the geometry yields a smaller device to generating a given intensity of light. The polarizer 86 can also be a film or sheet that follows the curved surface of the curved housing 90. The total power radiated from the illuminator 76 should be kept to a minimum to prevent accelerated tear evaporation. Light entering the pupil can cause reflex tearing, squinting, and other visual discomforts, all of which affect TFLT measurement accuracy. The polarizer 86 helps in this regard as the polarized light transmitted through the polarizer 86 is less intense than light emitted directly from the illuminator 76.

In order to prevent alteration of the proprioceptive senses and reduce heating of the tear film 102, incident power and intensity on the eye 72 may be minimized and thus, the step of collecting and focusing the specularly reflected light may carried out by the imaging device 80. The imaging device 80 may be a video camera, slit lamp microscope, or other observation apparatus mounted on the stand 78, as illustrated in FIGS. 6A and 6B. Detailed visualization of the image patterns of the tear film 102 involves collecting the specularly reflected light 84 and focusing the specularly reflected light at the lipid layer 106 such that the interference interactions of the specularly reflected light from the ocular tear film are observable.

Against the backdrop of the OSI device 70 in FIGS. 6A and 6B, FIG. 8 illustrates a flowchart discussing how the OSI device 70 can be used to obtain interference interactions of specularly reflected light from the tear film 102, which can be used to measure TFLT. Interference interactions of specularly reflected light from the tear film 102 are first obtained and discussed before measurement of TFLT is discussed. In this embodiment as illustrated in FIG. 8, the process starts by illuminating the patient with the illuminator 76 including the polarizer 86 (block 120), then adjusting the patient 74 with regard to the imaging device 80 (block 122). The illuminator 76 including the polarizer 86 is positioned to illuminate the patient's 74 tear film 102 (block 124). The imaging device 80 is controlled to be focused on the anterior surface 108 of the lipid layer 106 such that the interference interactions of specularly reflected light from the tear film 102 are observable (block 126). The imaging device 80 is then controlled and focused on the lipid layer 106 to collect specularly reflected light from an area or region of interest on a tear film as a result of illuminating the tear film with the illuminator 76 in an image (block 128, FIG. 8).

As illustrated in FIG. 9, an exemplary image 130 of a patient's eye 132 is shown that has been illuminated with the illuminator 76 including the polarizer 86. The illuminator 76 and the imaging device 80 may be controlled to illuminate an area or region of interest 134 on a tear film 136 that does not include a pupil 138 of the eye 132 so as to reduce reflex tearing. Reflex tearing will temporarily lead to thicker aqueous and lipid layers, thus temporarily altering the interference signals of specularly reflected light from the tear film 136. As shown in FIG. 9, when the imaging device 80 is focused on an anterior surface 142 of the lipid layer 144 of the tear film 136, interference interactions 140 of the interference signal of the specularly reflected light from the tear film 136 as a result of illumination by the illuminator 76 are captured in the area or region of interest 134 in the image 130. The interference interactions 140 appear to a human observer as colored patterns as a result of the wavelengths present in the interference of the specularly reflected light from the tear film 136.

However, the background signal is also captured in the image 130. The background signal is added to the specularly reflected light in the area or region of interest 134 and included outside the area or region of interest 134 as well. Background signal is light that is not specularly reflected from the tear film 136 and thus contains no interference information. The background signal can include stray and ambient light entering into the imaging device 80, scattered light from the patient's 74 face, eyelids, and/or eye 132 structures outside and beneath the tear film 136 as a result of stray light, ambient light and diffuse illumination by the illuminator 76, and images of structures beneath the tear film 136. For example, the image 130 includes the iris of the eye 132 beneath the tear film 136. Background signal adds a bias (i.e., offset) error to the captured interference of specularly reflected light from the tear film 136 thereby reducing its signal strength and contrast. Further, if the background signal has a color hue different from the light of the light source, a color shift can also occur to the interference of specularly reflected light from the tear film 136 in the image 130. The imaging device 80 produces a output signal that represents the light rays captured in the image 130. Because the image 130 contains light rays from specularly reflected light as well as the background signal, the output signal produced by the imaging device 80 from the image 130 will contain an interference signal representing the captured interference of the specularly reflected light from the tear film 136 with a bias (i.e., offset) error caused by the background signal. As a result, the output signal analyzed to measure TFLT may contain error as a result of the background signal bias (i.e., offset) error.

Thus, in this embodiment, the polarizer 86 is utilized to attenuate the unpolarized light emitted from the illuminator 76 thereby increasing a ratio of the specularly reflected light to the background signal comprised of the unpolarized light returned from the ROI 134 of the tear film 136. In this manner, the background signal is reduced to a point that the specularly reflected light containing the optical wave interference from the ROI of the ocular tear film is prominent enough to be produced and processed.

After the interference of the specularly reflected light is captured and a resulting signal containing the interference signal is produced and processed, the interference signal or representations thereof can be compared against a tear film layer interference model to measure TFLT. The interference signal can be processed and converted by the imaging device into digital red-green-blue (RGB) component values which can be compared to RGB component values in a tear film interference model to measure tear film TFLT. The tear film interference model is based on modeling the lipid layer of the tear film in various LLTs and representing resulting interference interactions in the interference signal of specularly reflected light from the tear film model when illuminated by the light source. The tear film interference model can be a theoretical tear film interference model where the particular light source, the particular imaging device, and the tear film layers are modeled mathematically, and the resulting interference signals for the various LLTs recorded when the modeled light source illuminates the modeled tear film layers recorded using the modeled imaging device. The settings for the mathematically modeled light source and imaging device should be replicated in the illuminator 76 and imaging device 80 used in the OSI device 70. Alternatively, the tear film interference model can be based on a phantom tear film model, comprised of physical phantom tear film layers wherein the actual light source is used to illuminate the phantom tear film model and interference interactions in the interference signal representing interference of specularly reflected light are empirically observed and recorded using the actual imaging device.

The aqueous layer may be modeled in the tear film interference model to be of an infinite, minimum, or varying thickness. If the aqueous layer is modeled to be of an infinite thickness, the tear film interference model assumes no specular reflections occur from the aqueous-to-mucin layer transition 118 (see FIG. 7). If the aqueous layer 116 is modeled to be of a certain minimum thickness (e.g., ≧2 μm), the specular reflection from the aqueous-to-mucin layer transition 118 may be considered negligible on the effect of the convolved RGB signals produced by the interference signal. In either case, the tear film interference model will only assume and include specular reflections from the lipid-to-aqueous layer transition 112. Thus, these tear film interference model embodiments allow measurement of LLT regardless of ALT. The interference interactions in the interference signal are compared to the interference interactions in the tear film interference model to measure LLT.

Alternatively, if the aqueous layer 116 is modeled to be of varying thicknesses, the tear film interference model additionally includes specular reflections from the aqueous-to-mucin layer transition 118 in the interference interactions. As a result, the tear film interference model will include two-dimensions of data comprised of interference interactions corresponding to various LLT and ALT combinations. The interference interactions from the interference signal can be compared to interference interactions in the tear film interference model to measure both LLT and ALT. More information regarding specific tear film interference models will be described later in this application.

Alternatively, a small-scale scanning of the ocular tear film can be employed to obtain interference of specularly reflected light from the tear film to obtain a high signal strength and contrast of an interference signal. For example, the area or region of interest imaged on the ocular tear film could be made very small down to the lowest resolution of the imaging device 80 (e.g., one pixel). In this manner, virtually no diffuse illumination is provided from the illuminator 76 to the area or region of interest on the patient's tear film when illuminated. Background signal captured in the image of the specularly reflected light from the tear film would be negligible compared to the level of specularly reflected light captured in the image. Thus, no subtraction of multiple images may need to be performed. The illuminator 76 would be controlled to scan the desired portions of the tear film for sequential image capture, with each scan capturing an image of specularly reflected light from a small area or region of interest. Each scanned image can then be assembled to produce an overall image of specularly reflected light from the tear film with negligible background signal and processed and analyzed to measure TFLT.

Exemplary OSI Devices

The above discussed illustrations provide examples of illuminating and imaging a patient's TFLT. These principles are described in more detail with respect to a specific example of an OSI device 170 illustrated in FIGS. 10A-46 and described below throughout the remainder of this application. The OSI device 170 can illuminate a patient's tear film, capture interference information from the patient's tear film, and process and analyze the interference information to measure TFLT. Further, the OSI device 170 includes a number of optional pre-processing features that may be employed to process the interference signal in the resulting signal to enhance TFLT measurement. The OSI device 170 may include a display and user interface to allow a physician or technician to control the OSI device 170 to image a patient's eye and tear film and measure the patient's TFLT.

Illumination and Imaging with Polarizer in Imaging Path

In this regard FIGS. 10A and 10B depict an OSI device 170, which comprises a multi-wavelength light source 146 that is configured to direct a multi-wavelength light including unpolarized light having a first intensity in an illumination path to illuminate a region of interest (ROI) of an ocular tear film of eye 192, thereby producing a specularly reflected light in a polarization plane containing optical wave interference from the ROI of the ocular tear film. A polarizer 148 is disposed in the illumination path with a polarization axis 150 parallel or substantially parallel to the polarization plane of the specularly reflected light to cause a background signal comprised of unpolarized light returned from the ROI of the ocular tear film to have a second intensity less than the first intensity. An imaging device 152 is configured to capture the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film. The background signal includes unpolarized light from the ocular tear film comprising at least a portion of the background signal. The polarizer 148 attenuates the unpolarized light thereby increasing a ratio of the specularly reflected light to the background signal comprised of the unpolarized light returned from the ROI of the ocular tear film. Moreover, the polarizer 148 decreases the intensity of the background signal comprised of unpolarized light returned from the ROI of the ocular tear film as compared to the intensity of the background signal if the polarizer were not disposed in the illumination path.

The OSI device 170 further comprises a second polarizer 154 disposed in an imaging path of the imaging device 152. The second polarizer 154 has a polarization axis 156 aligned parallel or substantially parallel with the specularly reflected light in the first polarization plane from the ROI of the ocular tear film. Unpolarized light making up a background signal is reduced by at least 50 percent compared to utilization of the polarizer 148 alone. Moreover, the second polarizer 154 combined with the polarizer 148 provides a ratio of specularly reflected light intensity from the ocular tear film to background signal intensity is at least 400 percent. As shown in FIG. 9, when the imaging device 80 is focused on an anterior surface 142 of the lipid layer 144 of the tear film 136, interference interactions 140 of the interference signal of the specularly reflected light from the tear film 136 as a result of illumination by the illuminator 76 are captured in the area or region of interest 134 in the image 130. The interference interactions 140 appear to a human observer as colored patterns as a result of the wavelengths present in the interference of the specularly reflected light from the tear film 136. However, in this case the interference of the specularly reflected light from the tear film 136 is more prominent and better isolated over utilizing the polarizer 148 alone.

OSI Device Inside Housing with Display

FIG. 12 illustrates a perspective view of the OSI device 170 in a commercial configuration. The OSI device 170 is designed to facilitate imaging of the patient's ocular tear film and processing and analyzing the images to determine characteristics regarding a patient's tear film. The OSI device 170 includes an imaging device and light source in this regard, as will be described in more detail below. As illustrated in FIG. 12, the OSI device 170 is comprised generally of a housing 172, a display monitor (“display”) 174, and a patient head support 176. The housing 172 may be designed for table top placement. The housing 172 rests on a base 178 in a fixed relationship. As will be discussed in more detail below, the housing 172 houses an imaging device and other electronics, hardware, and software to allow a clinician to image a patient's ocular tear film. A light source 173 (also referred to herein as “illuminator 173”) is also provided in the housing 172 and provided behind a diffusing translucent window 175. The translucent window 175 may be a flexible, white, translucent acrylic plastic sheet.

To image a patient's ocular tear film, the patient places his or her head in the patient head support 176 and rests his or her chin on a chin rest 180. The chin rest 180 can be adjusted to align the patient's eye and tear film with the imaging device inside the housing 172, as will be discussed in more detail below. The chin rest 180 may be designed to support up to two (2) pounds of weight, but such is not a limiting factor. A transparent window 177 allows the imaging device inside the housing 172 to have a clear line of sight to a patient's eye and tear film when the patient's head is placed in the patient head support 176. The OSI device 170 is designed to image one eye at a time, but can be configured to image both eyes of a patient, if desired.

In general, the display 174 provides input and output from the OSI device 170. For example, a user interface can be provided on the display 174 for the clinician to operate the OSI device 170 and to interact with a control system provided in the housing 172 that controls the operation of the OSI device 170, including an imaging device, an imaging device positioning system, a light source, other supporting hardware and software, and other components. For example, the user interface can allow control of imaging positioning, focus of the imaging device, and other settings of the imaging device for capturing images of a patient's ocular tear film. The control system may include a general purpose microprocessor or computer with memory for storage of data, including images of the patient's eye and tear film. The microprocessor should be selected to provide sufficient processing speed to process images of the patient's tear film and generate output characteristic information about the tear film (e.g., one minute per twenty second image acquisition). The control system may control synchronization of activation of the light source and the imaging device to capture images of areas of interest on the patient's ocular tear film when properly illuminated. Various input and output ports and other devices can be provided, including but not limited to a joystick for control of the imaging device, USB ports, wired and wireless communication including Ethernet communication, a keyboard, a mouse, speaker(s), etc. A power supply is provided inside the housing 172 to provide power to the components therein requiring power. A cooling system, such as a fan, may also be provided to cool the OSI device 170 from heat generating components therein.

The display 174 is driven by the control system to provide information regarding a patient's imaged tear film, including TFLT. The display 174 also provides a graphical user interface (GUI) to allow a clinician or other user to control the OSI device 170. To allow for human diagnosis of the patient's tear film, images of the patient's ocular tear film taken by the imaging device in the housing 172 can also be displayed on the display 174 for review by a clinician, as will be illustrated and described in more detail below. The images displayed on the display 174 may be real-time images being taken by the imaging device, or may be previously recorded images stored in memory. To allow for different orientations of the OSI device 170 to provide a universal configuration for manufacturing, the display 174 can be rotated about the base 178. The display 174 is attached to a monitor arm 182 that is rotatable about the base 178, as illustrated. The display 174 can be placed opposite of the patient head support 176, as illustrated in FIG. 12, if the clinician desires to sit directly across from the patient. Alternatively, display 174 can be rotated either left or right about the X-axis to be placed adjacent to the patient head support 176. The display 174 may be a touch screen monitor to allow a clinician or other user to provide input and control to the control system inside the housing 172 directly via touch of the display 174 for control of the OSI device 170. The display 174 illustrated in FIG. 12 is a fifteen inch (15″) flat panel liquid crystal display (LCD). However, the display 174 may be provided of any type or size, including but not limited to a cathode ray tube (CRT), plasma, LED, OLED, projection system, etc.

FIG. 13 illustrates a side view of the OSI device 170 of FIG. 12 to further illustrate imaging of a patient's eye and ocular tear film. As illustrated therein, a patient places their head 184 in the patient head support 176. More particularly, the patient places their forehead 186 against a headrest 188 provided as part of the patient head support 176. The patient places their chin 190 in the chin rest 180. The patient head support 176 is designed to facilitate alignment of a patient's eye 192 with the OSI device 170, and in particular, an imaging device 152 (and illuminator) shown as being provided inside the housing 172. The chin rest 180 can be adjusted higher or lower to move the patient's eye 192 with respect to the OSI device 170.

OSI Device Employing Rotatable Polarizer Holder

FIGS. 14A and 14B depict the OSI device 170 further configured to include a rotatable holder 194 that holds the second polarizer 154 such that it is selectively disposable between a first position within an imaging path of the imaging device and a second position outside the imaging path of the imaging device. An aperture 195 is also selectively disposable within the imaging path so that images may be captured without using the second polarizer 154. The rotatable holder 194 is coupled to an electric motor 196 that selectively disposes the second polarizer between the first position and the second position.

As further shown in FIGS. 14A and 14B, the imaging device 152 can be used to image the patient's ocular tear film to determine characteristics of the patient's tear film. In particular, the imaging device 152 is used to capture interference interactions of the specularly reflected light from the patient's tear film when illuminated by the light source 146 (also referred to herein as “illuminator 146”) as well as background signal. In the OSI device 170, the imaging device 152 is the “The Imaging Source” model DFK21BU04 charge coupling device (CCD) digital video camera 198, but many types of metrological grade cameras or imaging devices can be provided. A CCD camera enjoys characteristics of efficient light gathering, linear behavior, cooled operation, and immediate image availability. A linear imaging device is one that provides an output signal representing a captured image which is precisely proportional to the input signal from the captured image. Thus, use of a linear imaging device (e.g., gamma correction set to 1.0, or no gamma correction) provides undistorted interference data which can then be analyzed using linear analysis models. In this manner, the resulting images of the tear film do not have to be linearized before analysis, thus saving processing time. Gamma correction can then be added to the captured linear images for human-perceptible display on the non-linear display 174 (FIGS. 12 and 13) in the OSI device 170. Alternatively, the opposite scenario could be employed. That is, a non-linear imaging device or non-linear setting would be provided to capture tear film images, wherein the non-linear data representing the interference interactions of the interference signal can be provided to a non-linear display monitor without manipulation to display the tear film images to a clinician. The non-linear data would be linearized for tear film processing and analysis to estimate tear film layer thickness.

The video camera 198 is capable of producing lossless full motion video images of the patient's eye. As illustrated in FIGS. 14A and 14B, the video camera 198 has a depth of field defined by the angle between rays 199 and the lens focal length that allows the patient's entire tear film to be in focus simultaneously. The video camera 198 has an external trigger support so that the video camera 198 can be controlled by a control system to image the patient's eye. The video camera 198 includes a lens that fits within the housing 172. The video camera 198 in this embodiment has a resolution of 640×480 pixels and is capable of frame rates up to sixty (60) frames per second (fps). The lens system employed in the video camera 198 images a 16×12 mm dimension in a sample plane onto an active area of a CCD detector within the video camera 198. As an example, the video camera 198 may be the DBK21AU04 Bayer VGA (640×480) video camera using a Pentax VS-LD25 Daitron 25-mm fixed focal length lens. Other camera models with alternate pixel size and number, alternate lenses, (etc) may also be employed.

Although a video camera 198 is provided in the OSI device 170, a still camera could also be used if the frame rate is sufficiently fast enough to produce high quality images of the patient's eye. High frame rate in frames per second (fps) facilitate high quality captured interference signal representing specularly reflected light from a patient's tear film, and may provide less temporal (i.e., motion) artifacts (e.g., motion blurring) in captured images, resulting in high quality captured images. This is especially the case since the patient's eye may move irregularly as well as blinking, obscuring the tear film from the imaging device during examination.

A camera positioning system 200 is also provided in the housing 172 of the OSI device 170 to position the video camera 198 for imaging of the patient's tear film. The camera positioning system 200 is under the control of a control system. In this manner, a clinician can manipulate the position of the video camera 198 to prepare the OSI device 170 to image the patient's tear film. The camera positioning system 200 allows a clinician and/or control system to move the video camera 198 between different patients' eyes 192, but can also be designed to limit the range of motion within designed tolerances. The camera positioning system 200 also allows for fine tuning of the video camera 198 position. The camera positioning system 200 includes a stand 202 attached to a base 204. A linear servo or actuator 206 is provided in the camera positioning system 200 and connected between the stand 202 and a camera platform 207 supporting the video camera 198 to allow the video camera 198 to be moved in the vertical (i.e., Y-axis) direction.

In this embodiment of the OSI device 170, the camera positioning system 200 may not allow the video camera 198 to be moved in the X-axis or the Z-axis (in and out of FIGS. 14A and 14B), but the invention is not so limited. The illuminator 146 is also attached to the camera platform 207 such that the illuminator 146 maintains a fixed geometric relationship to the video camera 198. Thus, when the video camera 198 is adjusted to the patient's eye 192, the illuminator 146 is automatically adjusted to the patient's eye 192 in the same regard as well. This may be important to enforce a desired distance (d) and angle of illumination (Φ) of the patient's eye 192, as illustrated in FIGS. 14A and 14B, to properly capture the interference interactions of the specularly reflected light from the patient's tear film at the proper angle of incidence according to Snell's law, since the OSI device 170 is programmed to assume a certain distance and certain angles of incidence. In the OSI device 170 in FIGS. 14A and 14B, the angle of illumination (Φ) of the patient's eye 192 relative to the video camera 198 axis is approximately 30 degrees at the center of the illuminator 146 and includes a relatively large range of angles from about 5 to 60 degrees, but any angle may be provided.

Illuminator Detail

FIGS. 15-17 provide more detail on the illuminator 146. As illustrated in FIG. 15, the exemplary illuminator 146 is provided on an arced surface 208 (see also, FIGS. 15-17) of approximately 75 degrees to provide a large area, broad spectrum light source covering the visible regions of approximately 400 nanometers (nm) to 700 nm. In this embodiment, the arced surface 208 has a radius to an imaginary center of approximately 190 mm (“r” in FIG. 15) and has a face 250 mm high by 100 mm wide. The arced surface 208 could be provided as a flat surface, but an arced surface may allow for: better illumination uniformity, a smaller sized illuminator 146 for packaging constraints, while providing the same effective illumination area capability. In this example, the illuminator 146 is a Lambertian emitter wherein the light emitter has approximately the same intensity in all directions; however, the present invention is not so limited. The illuminator 146 is arranged so that, from the perspective of the video camera 198, emitted light rays are specularly reflected from the tear film of the patient's eye 192 and undergo constructive and destructive interference in the lipid layer and layers beneath the lipid layer. In this embodiment, the illuminator 146 is comprised of high efficiency, white light emitting diodes (LEDs) 210 (see FIGS. 15 and 16) mounted on a printed circuit board (PCB) 212 (FIG. 16), wherein each LED 210 or each grouping of LEDs is independently addressable by the control system to be turned on and off. Supporting circuitry (not shown) may be included to control operation of the LEDs 210, and to automatically shut off the LEDs 210 when the OSI device 170 is not in use. Each LED 210 has a 120 degree (“Lambertian”) forward projection angle, a 1350 mcd maximum intensity, manufactured by LEDtronics. Other light sources other than LEDs are also possible, including but not limited to lasers, incandescent light, and organic LEDs (OLEDs), as examples. Further, the light source is not required to be a Lambertian emitter. For example, the light emitted from the light source may be collimated.

As illustrated in FIG. 17, the PCB 212 is placed inside an illuminator housing 214. The illuminator housing 214 is comprised of two side panels 216A, 216B that are disposed on opposite sides of the arced surfaced 208 when held by base and top panels 218, 220, and also includes a rear panel 222. The arced surface 208 is comprised of a diffuser 209 to diffuse the light emitted by the LEDs 210. The diffuser 209 can be selected to minimize intensity reduction, while providing sufficient scattering to make the illumination uniform light wave fall off on the light emitted by the outside LEDs 210. The diffuser 209, PCB 212, and rear panel 222 are flexible and fit within grooves 223 located in the top and base panels 220, 218, and grooves 224 located in the side panels 216A, 216B. The illuminator housing 214 is snapped together and the side panels 216A, 216B are then screwed to the top and base panels 220, 218.

The diffuser 209 may also be comprised of more than one diffuser panel to improve uniformity in the light emitted from the illuminator 146. The side panels 216A, 216B and the base and top panels 218, 220 form baffles around the PCB 212 and the LEDs 210. The inside of these surfaces may contain a reflective film (e.g., 3M ESR film) to assist in the uniformity of light emitted by the LEDs 210. The reflective film may assist in providing a uniform light intensity over an entire area or region of interest on a patient's tear film. This may be particularly an issue on the outer edges of the illumination pattern.

System Level

Now that the imaging and illumination functions of the OSI device 170 have been described, FIG. 18A illustrates a system level diagram illustrating more detail regarding the control system and other internal components of the OSI device 170 provided inside the housing 172 according to one embodiment to capture images of a patient's tear film and process those images. As illustrated therein, a control system 240 is provided that provides the overall control of the OSI device 170. The control system 240 may be provided by any microprocessor-based or computer system. The control system 240 illustrated in FIG. 18A is provided in a system-level diagram and does not necessarily imply a specific hardware organization and/or structure. As illustrated therein, the control system 240 contains several systems. A polarization settings system 241 may be provided that accepts polarization settings from a clinician user. A camera settings system 242 may be provided that accepts camera settings from a clinician user. Exemplary camera settings 244 are illustrated, but may be any type according to the type and model of camera provided in the OSI device 170 as is well understood by one of ordinary skill in the art. The polarization settings can be derived from the camera settings 244. For example, a camera and polarization synchronization setting pertaining to the rotatable holder 194 (FIGS. 14A and 14B) can be derived from the camera settings 244.

The camera settings 244 may be provided to (The Imaging Source) camera drivers 246, which may then be loaded into the video camera 198 upon initialization of the OSI device 170 for controlling the settings of the video camera 198. The settings and drivers may be provided to a buffer 248 located inside the video camera 198 to store the settings for controlling a CCD 250 for capturing ocular image information from a lens 252. Ocular images captured by the lens 252 and the CCD 250 are provided to a de-Bayering function 254 which contains an algorithm for post-processing of raw data from the CCD 250 as is well known. The ocular images are then provided to a video acquisition system 256 in the control system 240 and stored in memory, such as random access memory (RAM) 258. The stored ocular images or signal representations can then be provided to a pre-processing system 260 and a post-processing system 262 to manipulate the ocular images to obtain the interference interactions of the specularly reflected light from the tear film and analyze the information to determine characteristics of the tear film. Pre-processing settings 264 and post-processing settings 266 can be provided to the pre-processing system 260 and post-proces sing system 262, respectively, to control these functions. These settings 264, 266 will be described in more detail below. The post-processed ocular images and information may also be stored in mass storage, such as disk memory 268, for later retrieval and viewing on the display 174.

The control system 240 may also contain a visualization system 270 that provides the ocular images to the display 174 to be displayed in human-perceptible form on the display 174. Before being displayed, the ocular images may have to be pre-processed in a pre-processing video function 272. For example, if the ocular images are provided by a linear camera, non-linearity (i.e. gamma correction) may have to be added in order for the ocular images to be properly displayed on the display 174. Further, contrast and saturation display settings 274, which may be controlled via the display 174 or a device communicating to the display 174, may be provided by a clinician user to control the visualization of ocular images displayed on the display 174. The display 174 is also adapted to display analysis result information 276 regarding the patient's tear film, as will be described in more detail below. The control system 240 may also contain a user interface system 278 that drives a graphical user interface (GUI) utility 280 on the display 174 to receive user input 282. The user input 282 can include any of the settings for the OSI device 170, including the camera settings 244, the pre-processing settings 264, the post-processing settings 266, the display settings 274, the visualization system 270 enablement, and video acquisition system 256 enablement, labeled 1-6. The GUI utility 280 may only be accessible by authorized personnel and used for calibration or settings that would normally not be changed during normal operation of the OSI device 170 once configured and calibrated.

Overall Process Flow

FIG. 18B illustrates an exemplary overall flow process performed by the OSI device 170 for capturing tear film images from a patent and analysis for TFLT measurement. As illustrated in FIG. 18B, the video camera 198 is connected via a USB port 283 to the control system 240 (see FIG. 18A) for control of the video camera 198 and for transferring images of a patient's tear film taken by the video camera 198 back to the control system 240. The control system 240 includes a compatible camera driver 246 to provide a transfer interface between the control system 240 and the video camera 198. Prior to tear film image capture, the configuration or camera settings 244 are loaded into the video camera 198 over the USB port 283 to prepare the video camera 198 for tear film image capture (block 285). Further, an audio video interleaved (AVI) container is created by the control system 240 to store video of tear film images to be captured by the video camera 198 (block 286). At this point, the video camera 198 and control system 240 are ready to capture images of a patient's tear film. The control system 240 waits for a user command to initiate capture of a patient's tear film (blocks 287, 288).

Once image capture is initiated (block 288), the control system enables image capture to the AVI container previously setup (block 286) for storage of images captured by the video camera 198 (block 289). The control system 240 controls the video camera 198 to capture images of the patient's tear film (block 289) until timeout or the user terminates image capture (block 290) and image capture halts or ends (block 291). Images captured by the video camera 198 and provided to the control system 240 over the USB port 283 are stored by the control system 240 in RAM 258(block 292).

The captured images of the patient's ocular tear film can subsequently be processed and analyzed to perform TFLT measurement, as described in more detail below and throughout the remainder of this disclosure. The processing can include simply displaying the patient's tear film or performing TFLT measurement (block 293). If the display option is selected to allow a technician to visually view the patient's tear film, display processing is performed (block 294) which can be the display processing 270 described in more detail below with regard to FIG. 27. For example, the control system 240 can provide a combination of images of the patient's tear film that show the entire region of interest of the tear film on the display 174. If TFLT measurement is desired, the control system 240 performs pre-processing of the tear film images for TFLT measurement (block 295), which can be the pre-processing system 260 described in more detail below with regard to FIG. 19. The control system 240 also performs post-processing of the tear film images for TFLT measurement (block 296), which can be the post-processing system 262 described in more detail below with regard to FIG. 29.

Pre-Processing

FIG. 19 illustrates an exemplary pre-processing system 260 for pre-processing ocular tear film images captured by the OSI device 170 for eventual analysis and TFLT measurement. In this system, the video camera 198 has already taken images of a patient's ocular tear film provided the images to the video acquisition system 256. The frames of the images were then loaded into RAM 258 by the video acquisition system 256. Thereafter, as illustrated in FIG. 19, the control system 240 commands the pre-processing system 260 to pre-process the images. An exemplary GUI utility 280 is illustrated in FIG. 20 that may be employed by the control system 240 to allow a clinician to operate the OSI device 170 and control pre-processing settings 264 and post-processing settings 266, which will be described later in this application. In this regard, the pre-processing system 260 loads the image frames of the ocular tear film from RAM 258 (block 300). The exemplary GUI utility 280 in FIG. 20 allows for a stored image file of previously stored video sequence of image frames captured by the video camera 198 by entering a file name in the file name field 351. A browse button 352 also allows searches of the memory for different video files, which can either be buffered by selecting a buffered box 354 or loaded for pre-processing by selecting the load button 356.

If the loaded image frames of the tear film are buffered, they can be played using display selection buttons 358, which will in turn display the images on the display 174. The images can be played on the display 174 in a looping fashion, if desired, by selecting the loop video selection box 360.

The image of the tear film illustrated in FIG. 21 was obtained with a DBK 21AU04 Bayer VGA (640×480) video camera having a Pentax VS-LD25 Daitron 25-mm fixed focal length lens with maximum aperture at a working distance of 120 mm and having the following settings, as an example:

-   -   Gamma=100 (to provide linearity with exposure value)     -   Exposure= 1/16 second     -   Frame rate=60 fps     -   Data Format=BY8     -   Video Format=−uncompressed, RGB 24-bit AVI     -   Hue=180 (neutral, no manipulation)     -   Saturation=128(neutral, no manipulation)     -   Brightness=0 (neutral, no manipulation)     -   Gain=260 (minimum available setting in this camera driver)     -   White balance=B=78; R=20.

Thresholding

Any number of optional pre-processing steps and functions can next be performed on the resulting combined tear film image(s), which will now be described. For example, an optional threshold pre-processing function may be applied to the resulting image or each image in a video of images of the tear film (e.g., FIG. 21) to eliminate pixels that have a difference signal below a threshold level (block 304 in FIG. 19). Image threshold provides a black and white mask (on/off) that is applied to the tear film image being processed to assist in removing residual information that may not be significant enough to be analyzed and/or may contribute to inaccuracies in analysis of the tear film. The threshold value used may be provided as part of a threshold value setting provided by a clinician as part of the pre-processing settings 264, as illustrated in the system diagram of FIG. 18A. For example, the GUI utility 280 in FIG. 20 includes a compute threshold selection box 372 that may be selected to perform thresholding, where the threshold brightness level can be selected via the threshold value slide 374. The tear film image of FIG. 21 is copied and converted to grayscale. The grayscale image has a threshold applied according to the threshold setting to obtain a binary (black/white) image that will be used to mask the tear film image of FIG. 21. After the mask is applied to the tear film image of FIG. 21, the new tear film image is stored in RAM 258. The areas of the tear film image that do not meet the threshold brightness level are converted to black as a result of the threshold mask.

FIGS. 22A and 22B illustrate examples of threshold masks for the tear film provided in FIG. 21. FIG. 22A illustrates a threshold mask 320 for a threshold setting of 70 counts out of a full scale level of 255 counts. FIG. 22B illustrates a threshold mask 322 for a threshold setting of 50. Note that the threshold mask 320 in FIG. 22A contains less portions of the tear film image, because the threshold setting is higher than for the threshold mask 322 of FIG. 22B. When the threshold mask according to a threshold setting of 70 is applied to the exemplary tear film image of FIG. 21, the resulting tear film image is illustrated FIG. 23. Much of the residual subtracted background image that surrounds the area or region of interest has been masked away.

Erode and Dilate

Another optional pre-processing function that may be applied to the resulting image or each image in a video of images of the tear film to correct anomalies in the tear film image(s) is the erode and dilate functions (block 306 in FIG. 19). The erode function generally removes small anomaly artifacts by subtracting objects with a radius smaller than an erode setting (which is typically in number of pixels) removing perimeter pixels where interference information may not be as distinct or accurate. The erode function may be selected by a clinician in the GUI utility 280 (see FIG. 20) by selecting the erode selection box 376. If selected, the number of pixels for erode can be provided in an erode pixels text box 378. Dilating generally connects areas that are separated by spaces smaller than a minimum dilate size setting by adding pixels of the eroded pixel data values to the perimeter of each image object remaining after the erode function is applied. The dilate function may be selected by a clinician in the GUI utility 280 (see FIG. 20) by providing the number of pixels for dilating in a dilate pixels text box 380. Erode and dilate can be used to remove small region anomalies in the resulting tear film image prior to analyzing the interference interactions to reduce or avoid inaccuracies. The inaccuracies may include those caused by bad pixels of the video camera 198 or from dust that may get onto a scanned image, or more commonly, spurious specular reflections such as: tear film meniscus at the juncture of the eyelids, glossy eyelash glints, wet skin tissue, etc. FIG. 24 illustrates the resulting tear film image of FIG. 23 after erode and dilate functions have been applied and the resulting tear film image is stored in RAM 258. As illustrated therein, pixels previously included in the tear film image that were not in the tear film area or region of interest are removed. This prevents data in the image outside the area or region of interest from affecting the analysis of the resulting tear film image(s).

Removing Blinks/Other Anomalies

Another optional pre-processing function that may be applied to the resulting image or each image in a video of images of the tear film to correct anomalies in the resulting tear film image is to remove frames from the resulting tear film image that include patient blinks or significant eye movements (block 308 in FIG. 19). As illustrated in FIG. 19, blink detection is shown as being performed after a threshold and erode and dilate functions are performed on the tear film image or video of images. Not pre-processing images where blinks are detected may increase the overall speed of pre-processing. The remove blinks or movement pre-processing may be selectable. For example, the GUI utility 280 in FIG. 20 includes a remove blinks selection box 384 to allow a user to control whether blinks and/or eye movements are removed from a resulting image or frames of the patient's tear film prior to analysis. Blinking of the eyelids covers the ocular tear film, and thus does not produce interference signals representing specularly reflected light from the tear film. If frames containing whole or partial blinks obscuring the area or region of interest in the patient's tear film are not removed, it would introduce errors in the analysis of the interference signals to determine characteristics of the TFLT of the patient's ocular tear film. Further, frames or data with significant eye movement between sequential images or frames can be removed during the detect blink pre-processing function.

Different techniques can be used to determine blinks in an ocular tear film image and remove the frames as a result. For example, in one embodiment, the control system 240 directs the pre-processing system 260 to review the stored frames of the resulting images of the tear film to monitor for the presence of an eye pupil using pattern recognition. A Hough Circle Transform may be used to detect the presence of the eye pupil in a given image or frame. If the eye pupil is not detected, it is assembled such that the image or frame contains an eye blink and thus should be removed or ignored during pre-processing from the resulting image or video of images of the tear film. The resulting image or video of images can be stored in RAM 258 for subsequent processing and/or analyzation.

In another embodiment, blinks and significant eye movements are detected using a histogram sum of the intensity of pixels in a resulting image of the tear film. An example of such a histogram 329 is illustrated in FIG. 25. The resulting image can be converted to grayscale (i.e., 255 levels) and a histogram generated with the gray levels of the pixels. In the histogram 329 of FIG. 25, the x-axis contains gray level ranges, and the number of pixels falling within each gray level is contained in the y-axis. The total of all the histogram 329 bins are summed. In the case of two identical frames, the histogram sum would be zero. However, even without an eye blink or significant eye movement, two sequentially captured frames of the patient's eye and the interference signals representing the specularly reflected light from the tear film are not identical. However, frame pairs with little movement will have a low histogram sum, while frame pairs with greater movement will yield a larger histogram sum. If the histogram sum is beyond a pre-determined threshold, an eye blink or large eye movement can be assumed and the image or frame removed. For example, the GUI utility 280 illustrated in FIG. 20 includes a histogram sum slide bar 386 that allows a user to set the threshold histogram sum. The threshold histogram sum for determining whether a blink or large eye movement should be assumed and thus the image removes from analysis of the patient's tear film can be determined experimentally, or adaptively over the course of a frame playback, assuming that blinks occur at regular intervals.

An advantage of a histogram sum of intensity method to detect eye blinks or significant eye movements is that the calculations are highly optimized as opposed to pixel-by-pixel analysis, thus assisting with real-time processing capability. Further, there is no need to understand the image structure of the patient's eye, such as the pupil or the iris details. Further, the method can detect both blinks and eye movements.

Another alternate technique to detect blinks in the tear film image or video of images for possible removal is to calculate a simple average gray level in an image or video of images. A blink contains skin color, which will increase the average gray level of an image containing a blink. A threshold average gray level setting can be provided. If the average gray level of a particular frame is below the threshold, the frame is ignored from further analysis or removed from the resulting video of frames of the tear film.

Another alternate technique to detect blinks in an image or video of images for removal is to calculate the average number of pixels in a given frame that have a gray level value below a threshold gray level value. If the percentage of pixels in a given frame is below a defined threshold percentage, this can be an indication that a blink has occurred in the frame, or that the frame is otherwise unworthy of consideration when analyzing the tear film. Alternatively, a spatial frequency calculation can be performed on a frame to determine the amount of fine detail in a given frame. If the detail present is below a threshold detail level, this may be an indication of a blink or other obscurity of the tear film, since skin from the eyelid coming down and being captured in a frame will have less detail than the image of the tear film. A histogram can be used to record any of the above-referenced calculations to use in analyzing whether a given frame should be removed from the final pre-processed resulting image or images of the tear film for analyzation.

ICC Profiling

Pre-processing of the resulting tear film image(s) may also optionally include applying an International Colour Consortium (ICC) profile to the pre-processed interference images of the tear film (block 310, FIG. 19). FIG. 26 illustrates an optional process of loading an ICC profile into an ICC profile 331 in the control system 240 (block 330). In this regard, the GUI utility 280 illustrated in FIG. 20 also includes an apply ICC box 392 that can be selected by a clinician to load the ICC profile 331. The ICC profile 331 may be stored in memory in the control system 240, including in RAM 258. In this manner, the GUI utility 280 in FIG. 20 also allows for a particular ICC profile 331 to be selected for application in the ICC profile file text box 394. The ICC profile 331 can be used to adjust color reproduction from scanned images from cameras or other devices into a standard red-green-blue (RGB) color space (among other selectable standard color spaces) defined by the ICC and based on a measurement system defined internationally by the Commission Internationale de l'Eclairage (CIE). Adjusting the pre-processed resulting tear film interference images corrects for variations in the camera color response and the light source spectrum and allows the images to be compatibly compared with a tear film layer interference model to measure the thickness of a TFLT, as will be described later in this application. The tear film layers represented in the tear film layer interference model can be LLTs, ALTs, or both, as will be described in more detail below.

In this regard, the ICC profile 331 may have been previously loaded to the OSI device 170 before imaging of a patient's tear film and also applied to a tear film layer interference model when loaded into the OSI device 170 independent of imaging operations and flow. As will be discussed in more detail below, a tear film layer interference model in the form of a TFLT palette 333 containing color values representing interference interactions from specularly reflected light from a tear film for various LLTs and ALTs can also be loaded into the OSI device 170 (block 332 in FIG. 29). The tear film layer interference model 333 contains a series of color values that are assigned LLTs and/or ALTs based on a theoretical tear film layer interference model to be compared against the color value representations of interference interactions in the resulting image(s) of the patient's tear film. When applying the optional ICC profile 331 to the tear film layer interference model 333 (block 334 in FIG. 26), the color values in both the tear film layer interference model and the color values representing interference interactions in the resulting image of the tear film are adjusted for a more accurate comparison between the two to measure LLT and/or ALT.

Brightness

Also as an optional pre-processing step, brightness and red-green-blue (RGB) subtract functions may be applied to the resulting interference signals of the patient's tear film before post-processing for analysis and measuring TFLT is performed (blocks 312 and 314 in FIG. 19). The brightness may be adjusted pixel-by-pixel by selecting the adjust brightness selection box 404 according to a corresponding brightness level value provided in a brightness value box 406, as illustrated in the GUI utility 280 of FIG. 20. When the brightness value box 406 is selected, the brightness of each palette value of the tear film layer interference model 333 is also adjusted accordingly.

RGB Subtraction (Normalization)

The RGB subtract function subtracts a DC offset from the interference signal in the resulting image(s) of the tear film representing the interference interactions in the interference signal. An RGB subtract setting may be provided from the pre-processing settings 264 to apply to the interference signal in the resulting image of the tear film to normalize against. As an example, the GUI utility 280 in FIG. 20 allows an RGB offset to be supplied by a clinician or other technician for use in the RGB subtract function. As illustrated therein, the subtract RGB function can be activated by selecting the RGB subtract selection box 396. If selected, the individual RGB offsets can be provided in offset value input boxes 398. After pre-processing is performed, if any, on the resulting image, the resulting image can be provided to a post-processing system to measure TLFT (block 316), as discussed later below in this application.

Displaying Images

The resulting images of the tear film may also be displayed on the display 174 of the OSI device 170 for human diagnosis of the patient's ocular tear film. The OSI device 170 is configured so that a clinician can display and see the raw captured image of the patient's eye 192 by the video camera 198, the resulting images of the tear film before pre-processing, or the resulting images of the tear film after pre-processing. Displaying images of the tear film on the display 174 may entail different settings and steps. For example, if the video camera 198 provides linear images of the patient's tear film, the linear images must be converted into a non-linear format to be properly displayed on the display 174. In this regard, a process that is performed by the visualization system 270 according to one embodiment is illustrated in FIG. 27.

As illustrated in FIG. 27, the video camera 198 has already taken images of a patient's ocular tear film, and provided the images to the video acquisition system 256. The frames of the images were then loaded into RAM 258 by the video acquisition system 256. Thereafter, as illustrated in FIG. 27, the control system 240 commands the visualization system 270 to process the images to prepare them for being displayed on the display 174, 338. In this regard, the visualization system 270 loads the image frames of the ocular tear film from RAM 258 (block 335).

Again, for example, this processing could be performed using the Matlab® function “cvAbsDiff.” Before being displayed, the contrast and saturation levels for the resulting images can be adjusted according to contrast and saturation settings provided by a clinician via the user interface system 278 and/or programmed into the visualization system 270 (block 337). For example, the GUI utility 280 in FIG. 20 provides an apply contrast button 364 and a contrast setting slide 366 to allow the clinician to set the contrast setting in the display settings 274 for display of images on the display 174. The GUI utility 280 also provides an apply saturation button 368 and a saturation setting slide 369 to allow a clinician to set the saturation setting in the display settings 274 for the display of images on the display 174. The images can then be provided by the visualization system 270 to the display 174 for displaying (block 338 in FIG. 27). Also, any of the resulting images after pre-processing steps in the pre-processing system 260 can be provided to the display 174 for processing.

FIG. 28 illustrates an example of a tear film image that is displayed on the display 174 of the OSI device 170. FIG. 28 illustrates an image 339 of the patient's tear film captured by the video camera 198. This image is the same image as illustrated in FIG. 21 and previously described above, but processed from a linear output from the video camera 198 to be properly displayed on the display 174.

In this example, if frames in the image frames capture blinks or erratic movements, and these frames are eliminated in pre-processing, a further reduction in frames will occur during pre-processing from the number of images raw captured in images of the patient's tear film. Although these frames are eliminated from being further processed, they can be retained for visualization rendering a realistic and natural video playback. Further, by applying a thresholding function and erode and dilating functions, the number of non-black pixels which contain TLFT interference information is substantially reduced as well. Thus, the amount of pixel information that is processed by the post-processing system 262 is reduced, and may be on the order of 70% less information to process than the raw image capture information, thereby pre-filtering for the desired interference ROI and reducing or elimination potentially erroneous information as well as allowing for faster analysis due to the reduction in information.

At this point, the resulting images of the tear film have been pre-processed by the pre-processing system 260 according to whatever pre-processing settings 264 and pre-processing steps have been selected or implemented by the control system 240. The resulting images of the tear film are ready to be processed for analyzing and determining TFLT. In this example, this is performed by the post-processing system 262 in FIG. 18A and is based on the post-processing settings 266 also illustrated therein. An embodiment of the post-processing performed by the post-processing system 262 is illustrated in the flowchart of FIG. 29.

Tear Film Interference Models

As illustrated in FIG. 29, pre-processed images 343 of the resulting images of the tear film are retrieved from RAM 258 where they were previously stored by the pre-processing system 260. Before discussing the particular embodiment of the post-processing system 262 in FIG. 29, in general, to measure TFLT, the RGB color values of the pixels in the resulting images of the tear film are compared against color values stored in a tear film interference model that has been previously loaded into the OSI device 170 (see FIG. 26. The tear film layer interference model 333 may be stored as a TFLT palette containing RGB values representing interference colors for given LLTs and/or ALTs. The TFLT palette contains interference color values that represent TFLTs based on a theoretical tear film interference model in this embodiment. Depending on the TFLT palette provided, the interference color values represented therein may represent LLTs, ALTs, or both. An estimation of TFLT for each ROI pixel is based on this comparison. This estimate of TFLT is then provided to the clinician via the display 174 and/or recorded in memory to assist in diagnosing DES.

Before discussing embodiments of how the TFLTs are estimated from the pre-processed resulting image colored interference interactions resulting from specularly reflected light from the tear film, tear film interference modeling is first discussed. Tear film interference modeling can be used to determine an interference color value for a given TFLT to measure TFLT, which can include both LLT and/or ALT.

Although the interference signals representing specularly reflected light from the tear film are influenced by all layers in the tear film, the analysis of interference interactions due to the specularly reflected light can be analyzed under a 2-wave tear film model (i.e., two reflections) to measure LLT. A 2-wave tear film model is based on a first light wave(s) specularly reflecting from the air-to-lipid layer transition of a tear film and a second light wave specularly reflecting from the lipid layer-to-aqueous layer transition of the tear film. In the 2-wave model, the aqueous layer is effective ignored and treated to be of infinite thickness. To measure LLT using a 2-wave model, a 2-wave tear film model was developed wherein the light source and lipid layers of varying thicknesses were modeled mathematically. To model the tear-film interference portion, commercially available software, such as that available by FilmStar and Zemax as examples, allows image simulation of thin films for modeling. Relevant effects that can be considered in the simulation include refraction, reflection, phase difference, polarization, angle of incidence, and refractive index wavelength dispersion. For example, a lipid layer could be modeled as having an index of refraction of 1.48, or as a BK7 fused silica having an index of refraction of 1.52, or SiO₂ fused silica substrate having a 1.46 index of refraction, as non-limiting examples. A back material, such as Magnesium Oxide (MgO) having an index of refraction of 1.74, or Magnesium Flouride (MgF₂) having an index of refraction of 1.38, may be used to provide a 2-wave model of air/(BK7 fused silica or SiO₂)/(BK7, MgO or MgF₂) (e.g., 1.0/1.52/1.74 for air/BK7/MgO or 1.0/1.46/1.38 for air/SiO₂/MgF₂). To obtain the most accurate modeling results, the model can include the refractive index and wavelength dispersion values of biological lipid material and biological aqueous material, found from the literature, thus to provide a precise two-wave model of air/lipid/aqueous layers. Thus, a 2-wave tear film interference model allows measurement of LLT regardless of ALT.

Simulations can be mathematically performed by varying the LLT between 10 to 300 nm. As a second step, the RGB color values of the resulting interference signals from the modeled light source causing the modeled lipid layer to specularly reflected light and received by the modeled camera were determined for each of the modeled LLT. These RGB color values representing interference interactions in specularly reflected light from the modeled tear film were used to form a 2-wave model LLT palette, wherein each RGB color value is assigned a different LLT. The resulting image from the patient's tear film containing interference signals representing specularly reflected light are compared to the RGB color values in the 2-wave model LLT palette to measure LLT.

In another embodiment, a 3-wave tear film interference model may be employed to estimate LLT. A 3-wave tear film interference model does not assume that the aqueous layer is infinite in thickness. In an actual patient's tear film, the aqueous layer is not infinite. The 3-wave tear film interference model is based on both the first and second reflected light waves of the 2-wave model and additionally light wave(s) specularly reflecting from the aqueous-to-mucin layer and/or cornea transitions. Thus, a 3-wave tear film interference model recognizes the contribution of specularly reflected light from the aqueous-to-mucin layer and/or cornea transition that the 2-wave tear film interference model does not. To estimate LLT using a 3-wave tear film interference model, a 3-wave tear film model was previously constructed wherein the light source and a tear film of varying lipid and aqueous layer thicknesses were mathematically modeled. For example, a lipid layer could be mathematically modeled as a material having an index of refraction of 1.48 or as fused silica substrate (SiO₂), which has a 1.46 index of refraction, or as BK7 fused silica having an index of refraction of 1.52. Different thicknesses of the lipid layer can be simulated. A fixed thickness aqueous layer (e.g., >=2 μm) could be mathematically modeled as Magnesium Flouride (MgF₂) having an index of refraction of 1.38 or Magnesium Oxide (MgO) having an index of refraction of 1.74. A biological cornea could be mathematically modeled as fused silica with no dispersion, thereby resulting in a 3-wave model of air/SiO₂/MgF₂/SiO₂ (i.e., 1.0/1.46/1.38/1.46 with no dispersion) or air/BK7/MgO/BK7 (i.e., 1.0/1.52/1.74/1.52), as non-limited examples. As before, accurate results are obtained if the model can include the refractive index and wavelength dispersion values of biological lipid material, biological aqueous material, and cornea tissue, found from the literature, thus to provide a precise two-wave model of air/lipid/aqueous/cornea layers. The resulting interference interactions of specularly reflected light from the various LLT values and with a fixed ALT value are recorded in the model and, when combined with modeling of the light source and the camera, will be used to compare against interference from specularly reflected light from an actual tear film to measure LLT and/or ALT.

In another embodiment of the OSI device 170 and the post-processing system 262 in particular, a 3-wave tear film interference model is employed to estimate both LLT and ALT. In this regard, instead of providing either a 2-wave theoretical tear film interference model that assumes an infinite aqueous layer thickness or a 3-wave model that assumes a fixed or minimum aqueous layer thickness (e.g., ≧2 μm), a 3-wave theoretical tear film interference model is developed that provides variances in both LLT and ALT in the mathematical model of the tear film. Again, the lipid layer in the tear film model could be modeled mathematically as a material having an index of refraction of 1.48, as fused silica substrate (SiO₂) having a 1.46 index of refraction, or as BK7 fused silica having an index of refraction of 1.52 as non-limiting examples. The aqueous layer could be modeled mathematically as Magnesium Flouride (MgF₂) having an index of refraction of 1.38 or Magnesium Oxide (MgO) having an index of refraction of 1.74. A biological cornea could be modeled as fused silica with no dispersion, thereby resulting in a 3-wave model of air/SiO₂/MgF₂/SiO₂ (no dispersion) or air/BK7/MgO/BK7, as non-limiting examples. Once again, the most accurate results are obtained if the model can include the refractive index and wavelength dispersion values of biological lipid material, biological aqueous material, and cornea tissue, found from the literature, thus to provide a precise two-wave model of air/lipid/aqueous/cornea layers. Thus, a two-dimensional (2D) TFLT palette 430 (FIG. 30A) is produced for analysis of interference interactions from specularly reflected light from the tear film. One dimension of the TFLT palette 430 represents a range of RGB color values each representing a given theoretical LLT calculated by mathematically modeling the light source and the camera and calculating the interference interactions from specularly reflected light from the tear film model for each variation in LLT 434 in the tear film interference model. A second dimension of the TFLT palette 430 represents ALT also calculated by mathematically modeling the light source and the camera and calculating the interference interactions from specularly reflected light from the tear film interference model for each variation in ALT 432 at each LLT value 434 in the tear film interference model.

Post-Processing/TFLT Measurement

To measure TFLT, a spectral analysis of the resulting interference signal or image is performed during post-processing to calculate a TFLT. In one embodiment, the spectral analysis is performed by performing a look-up in a tear film interference model to compare one or more interference interactions present in the resulting interference signal representing specularly reflected light from the tear film to the RGB color values in the tear film interference model. In this regard, FIGS. 30A and 30B illustrate two examples of palette models for use in post-processing of the resulting image having interference interactions from specularly reflected light from the tear film using a 3-wave theoretical tear film interference model developed using a 3-wave theoretical tear film model. In general, an RGB numerical value color scheme is employed in this embodiment, wherein the RGB value of a given pixel from a resulting pre-processed tear film image of a patient is compared to RGB values in the 3-wave tear film interference model representing color values for various LLTs and ALTs in a 3-wave modeled theoretical tear film. The closest matching RGB color is used to determine the LLT and/or ALT for each pixel in the resulting signal or image. All pixels for a given resulting frame containing the resulting interference signal are analyzed in the same manner on a pixel-by-pixel basis. A histogram of the LLT and ALT occurrences is then developed for all pixels for all frames and the average LLT and ALT determined from the histogram (block 348 in FIG. 29).

FIG. 30A illustrates an exemplary TFLT palette 430 in the form of colors representing the included RGB color values representing interference of specularly reflected light from a 3-wave theoretical tear film model used to compared colors from the resulting image of the patient's tear film to estimate LLT and ALT. FIG. 30B illustrates an alternative example of a TFLT palette 430′ in the form of colors representing the included RGB color values representing interference of specularly reflected light from a 3-wave theoretical tear film model used to compare colors from the resulting image of the patient's tear film to estimate LLT and ALT. As illustrated in FIG. 31, the TFLT palette 430 contains a plurality of hue colors arranged in a series of rows 432 and columns 434. In this example, there are 144 color hue entries in the TFLT palette 430, with nine (9) different ALTs and sixteen (16) different LLTs in the illustrated TFLT palette 430, although another embodiment includes thirty (30) different LLTs. Providing any number of LLT and TFLT increments is theoretically possible. The columns 434 in the TFLT palette 430 contain a series of LLTs in ascending order of thickness from left to right. The rows 432 in the TFLT palette 430 contain a series of ALTs in ascending order of thickness from top to bottom. The sixteen (16) LLT increments provided in the columns 434 in the TFLT palette 430 are 25, 50, 75, 80, 90, 100, 113, 125, 138, 150, 163, 175, 180, 190, 200, and 225 nanometers (nm). The nine (9) ALT increments provided in the rows 432 in the TFLT palette 430 are 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 3.0 and 6.0 μm. As another example, as illustrated in FIG. 30B, the LLTs in the columns 434′ in the TFLT palette 430′ are provided in increments of 10 nm between 0 nm and 160 nm. The nine (9) ALT increments provided in the rows 432′ in the TFLT palette 430 are 0.3, 0.5, 0.08, 1.0, 1.3, 1.5, 1.8, 2.0 and 5.0 μm.

As part of a per pixel LLT analysis 344 provided in the post-processing system 262 in FIG. 29, for each pixel in each of the pre-processed resulting images of the area or region of interest in the tear film, a closest match determination is made between the RGB color of the pixel to the nearest RGB color in the TFLT palette 430 (block 345 in FIG. 29). The ALTs and LLTs for that pixel are determined by the corresponding ALT thickness in the y-axis of the TFLT palette 430, and the corresponding LLT thickness in the x-axis of the TFLT palette 430. As illustrated in FIG. 30A, the TFLT palette 430 colors are actually represented by RGB values. The pixels in each of the pre-processed resulting images of the tear film are also converted and stored as RGB values, although any other color representation can be used as desired, as long as the palette and the image pixel data use the same representational color space. FIG. 31 illustrates the TFLT palette 430 in color pattern form with normalization applied to each red-green-blue (RGB) color value individually. Normalizing a TFLT palette is optional. The TFLT palette 430 in FIG. 31 is displayed using brightness control (i.e., normalization, as previously described) and without the RGB values included, which may be more visually pleasing to a clinician if displayed on the display 174. The GUI utility 280 allows selection of different palettes by selecting a file in the palette file drop down 402, as illustrated in FIG. 20, each palette being specific to the choice of 2-wave vs. 3-wave mode, the chosen source's spectrum, and the chosen camera's RGB spectral responses. To determine the closest pixel color in the TFLT palette 430, a Euclidean distance color difference equation is employed to calculate the distance in color between the RGB value of a pixel from the pre-processed resulting image of the patient's tear film and RGB values in the TFLT palette 430 as follows below, although the present invention is not so limited:

Diff.=√/((Rpixel−Rpalette)²⁺(Gpixel−Gpalette)²⁺(Bpixel−Bpalette)²)

Thus, the color difference is calculated for all palette entries in the TFLT palette 430. The corresponding LLT and ALT values are determined from the color hue in the TFLT palette 430 having the least difference from each pixel in each frame of the pre-processed resulting images of the tear film. The results can be stored in RAM 258 or any other convenient storage medium. To prevent pixels without a close match to a color in the TFLT palette 430 from being included in a processed result of LLT and ALT, a setting can be made to discard pixels from the results if the distance between the color of a given pixel is not within the entered acceptable distance of a color value in the TFLT palette 430 (block 346 in FIG. 29). The GUI utility 280 in FIG. 20 illustrates this setting such as would be the case if made available to a technician or clinician. A distance range input box 408 is provided to allow the maximum distance value to be provided for a pixel in a tear film image to be included in LLT and ALT results. Alternatively, all pixels can be included in the LLT and ALT results by selecting the ignore distance selection box 410 in the GUI utility 280 of FIG. 20.

Each LLT and ALT determined for each pixel from a comparison in the TFLT palette 430 via the closest matching color that is within a given distance (if that post-processing setting 266 is set) or for all LLT and ALT determined values are then used to build a TFLT histogram. The TFLT histogram is used to determine a weighted average of the LLT and ALT values for each pixel in the resulting image(s) of the patient's tear film to provide an overall estimate of the patient's LLT and ALT. FIG. 32 illustrates an example of such a TFLT histogram 460. This TFLT histogram 440 may be displayed as a result of the shown LLT histogram selection box 400 being selected in the GUI utility 280 of FIG. 27. As illustrated therein, for each pixel within an acceptable distance, the TFLT histogram 440 is built in a stacked fashion with determined ALT values 444 stacked for each determined LLT value 442 (block 349 in FIG. 29). Thus, the TFLT histogram 440 represents LLT and ALT values for each pixel. A horizontal line separates each stacked ALT value 444 within each LLT bar.

One convenient way to determine the final LLT and ALT estimates is with a simple weighted average of the LLT and ALT values 442, 444 in the TFLT histogram 440. In the example of the TFLT histogram 440 in FIG. 32, the average LLT value 446 was determined to be 90.9 nm. The number of samples 448 (i.e., pixels) included in the TFLT histogram 440 was 31,119. The frame number 450 indicates which frame of the resulting video image is being processed, since the TFLT histogram 440 represents a single frame result. The maximum distance 452 between the color of any given pixel among the 31,119 pixels and a color in the TFLT palette 430 was 19.9, 20 may have been the set limit (Maximum Acceptable Palette Distance) for inclusion of any matches. The average distance 454 between the color of each of the 31,119 pixels and its matching color in the TFLT palette 430 was 7.8. The maximum distance 452 and average distance 454 values provide an indication of how well the color values of the pixels in the interference signal of the specularly reflected light from the patient's tear film match the color values in the TFLT palette 430. The smaller the distance, the closer the matches. The TFLT histogram 440 can be displayed on the display 174 to allow a clinician to review this information graphically as well as numerically. If either the maximum distance 452 or average distance 454 values are too high, this may be an indication that the measured LLT and ALT values may be inaccurate, or that the image normalization is not of the correct value. Further imaging of the patient's eye and tear film, or system recalibration can be performed to attempt to improve the results. Also, a histogram 456 of the LLT distances 458 between the pixels and the colors in the TFLT palette 430 can be displayed as illustrated in FIG. 33 to show the distribution of the distance differences to further assist a clinician in judgment of the results.

Other results can be displayed on the display 174 of the OSI device 170 that may be used by a physician or technician to judge the LLT and/or ALT measurement results. For example, FIG. 34 illustrates a threshold window 424 illustrating a (inverse) threshold mask 426 that was used during pre-processing of the tear film images. In this example, the threshold window 424 was generated as a result of the show threshold window selection box 382 being selected in the GUI utility 280 of FIG. 20. This may be used by a clinician to humanly evaluate whether the threshold mask looks abnormal. If so, this may have caused the LLT and ALT estimates to be inaccurate and may cause the clinician to discard the results and image the patient's tear film again. The maximum distance between the color of any given pixel among the 31,119 pixels and a color in the tflt palette 430 was 19.9 in this example.

FIG. 35 illustrates another histogram that may be displayed on the display 174 and may be useful to a clinician. As illustrated therein, a three-dimensional (3D) histogram plot 460 is illustrated. The clinician can choose whether the OSI device 170 displays this histogram plot 460 by selecting the 3D plot selection box 416 in the GUI utility 280 of FIG. 20, as an example, or the OSI device 170 may automatically display the histogram plot 460. The 3D histogram plot 460 is simply another way to graphically display the fit of the processed pixels from the pre-processed images of the tear film to the TFLT palette 430. The plane defined by the LLT 462 and ALT 464 axes represents the TFLT palette 430. The axis labeled “Samples” 466 is the number of pixels that match a particular color in the TFLT palette 430.

FIG. 36 illustrates a result image 428 of the specularly reflected light from a patient's tear film. However, the actual pixel value for a given area on the tear film is replaced with the determined closest matching color value representation in the TFLT palette 430 to a given pixel for that pixel location in the resulting image of the patient's tear film (block 347 in FIG. 29). This setting can be selected, for example, in the GUI utility 280 of FIG. 20. Therein, a “replace resulting image . . . ” selection box 412 is provided to allow a clinician to choose this option. Visually displaying interference interactions representing the closest matching color value to the interference interactions in the interference signal of the specularly reflected light from a patient's tear film in this manner may be helpful to determine how closely the tear film interference model matches the actual color value representing the resulting image (or pixels in the image).

Ambiguities can arise when calculating the nearest distance between an RGB value of a pixel from a tear film image and RGB values in a TFLT palette, such as TFLT palettes 430 and 430′ in FIGS. 30A and 30B as examples. This is because when the theoretical LLT of the TFLT palette is plotted in RGB space for a given ALT in three-dimensional (3D) space, the TFLT palette 469 is a locus that resembles a pretzel like curve, as illustrated with a 2-D representation in the exemplary TFLT palette locus 470 in FIG. 37. Ambiguities can arise when a tear film image RGB pixel value has close matches to the TFLT palette locus 470 at significantly different LLT levels. For example, as illustrated in the TFLT palette locus 470 in FIG. 37, there are three (3) areas of close intersection 472, 474, 476 between RGB values in the TFLT palette locus 470 even though these areas of close intersection 472, 474, 476 represent substantially different LLTs on the TFLT palette locus 470. This is due to the cyclical phenomenon caused by increasing orders of optical wave interference, and in particular, first order versus second order interference for the LLT range in the tear films. Thus, if an RGB value of a tear film image pixel is sufficiently close to two different LLT points in the TFLT palette locus 470, the closest RGB match may be difficult to match. The closest RGB match may be to an incorrect LLT in the TFLT palette locus 470 due to error in the camera and translation of received light to RGB values. Thus, it may be desired to provide further processing when determining the closest RGB value in the TFLT palette locus 470 to RGB values of tear film image pixel values when measuring TFLT.

In this regard, there are several possibilities that can be employed to avoid ambiguous RGB matches in a TFLT palette. For example, the maximum LLT values in a TFLT palette may be limited. For example, the TFLT palette locus 470 in FIG. 37 includes LLTs between 10 nm and 300 nm. If the TFLT palette locus 470 was limited in LLT range, such as 240 nm as illustrated in the TFLT palette locus 478 in FIG. 38, two areas of close intersection 474 and 476 in the TFLT palette 469 in FIG. 37 are avoided in the TFLT palette 469 of FIG. 38. This restriction of the LLT ranges may be acceptable based on clinical experience since most patients do not exhibit tear film colors above the 240 nm range and dry eye symptoms are more problematic at thinner LLTs. In this scenario, the limited TFLT palette 469 of FIG. 38 would be used as the TFLT palette in the post-processing system 262 in FIG. 29, as an example.

Even by eliminating two areas of close intersection 474, 476 in the TFLT palette 469, as illustrated in FIG. 38, the area of close intersection 472 still remains in the TFLT palette locus 478. In this embodiment, the area of close intersection 472 is for LLT values near 20 nm versus 180 nm. In these regions, the maximum distance allowed for a valid RGB match is restricted to a value of about half the distance of the TFLT palette's 469 nearing ambiguity distance. In this regard, RGB values for tear film pixels with match distances exceeding the specified values can be further excluded from the TFLT calculation to avoid tear film pixels having ambiguous corresponding LLT values for a given RGB value to avoid error in TFLT measurement as a result.

In this regard, FIG. 39 illustrates the TFLT palette locus 478 in FIG. 38, but with a circle of radius R swept along the path of the TFLT palette locus 478 in a cylinder or pipe 480 of radius R. Radius R is the acceptable distance to palette (ADP), which can be configured in the control system 240. When visualized as a swept volume inside the cylinder or pipe 480, RGB values of tear film image pixels that fall within those intersecting volumes may be considered ambiguous and thus not used in calculating TFLT, including the average TFLT. The smaller the ADP is set, the more poorly matching tear film image pixels that may be excluded in TFLT measurement, but less pixels are available for use in calculation of TFLT. The larger the ADP is set, the less tear film image pixels that may be excluded in TFLT measurement, but it is more possible that incorrect LLTs are included in the TFLT measurement. The ADP can be set to any value desired. Thus, the ADP acts effectively as a filter to filter out RGB values for tear film images that are deemed a poor match and those that may be ambiguous according to the ADP setting. This filtering can be included in the post-processing system 262 in FIG. 29, as an example, and in step 346 therein, as an example.

Graphical User Interface (GUI)

In order to operate the OSI device 170, a user interface program may be provided in the user interface system 278 (see FIG. 18A) that drives various graphical user interface (GUI) screens on the display 174 of the OSI device 170 in addition to the GUI utility 280 of FIG. 20 to allow access to the OSI device 170. Some examples of control and accesses have been previously described above. Examples of these GUI screens from this GUI are illustrated in FIGS. 44-46 and described below. The GUI screens allow access to the control system 240 in the OSI device 170 and to features provided therein. As illustrated in FIG. 40, a login GUI screen 520 is illustrated. The login GUI screen 520 may be provided in the form of a GUI window 521 that is initiated when a program is executed. The login GUI screen 520 allows a clinician or other user to log into the OSI device 170. The OSI device 170 may have protected access such that one must have an authorized user name and password to gain access. This may be provided to comply with medical records and privacy protection laws. As illustrated therein, a user can enter their user name in a user name text box 522 and a corresponding password in the password text box 524. A touch or virtual keyboard 526 may be provided to allow alphanumeric entry. To gain access to help or to log out, the user can select the help and log out tabs 528, 530, which may remain resident and available on any of the GUI screens. After the user is ready to login, the user can select the submit button 532. The user name and password entered in the user name text box 522 and the password text box 524 are verified against permissible users in a user database stored in the disk memory 268 in the OSI device 170 (see FIG. 18A).

If a user successfully logs into the OSI device 170, a patient GUI screen 534 appears on the display 174 with the patient records tab 531 selected, as illustrated in FIG. 41. The patient GUI screen 534 allows a user to either create a new patient or to access an existing patient. A new patient or patient search information can be entered into any of the various patient text boxes 536 that correspond to patient fields in a patient database. Again, the information can be entered through the virtual keyboard 526, facilitated with a mouse pointing device (not shown), a joystick, or with a touch screen covering on the display 174. These include a patient ID text box 538, patient last name text box 540, patient middle initial text box 542, a patient first name text box 544, and a date of birth text box 546. This data can be entered for a new patient, or used to search a patient database on the disk memory 268 (see FIG. 18A) to access an existing patient's records. The OSI device 170 may contain disk memory 268 with enough storage capability to store information and tear film images regarding a number of patients. Further, the OSI device 170 may be configured to store patient information outside of the OSI device 170 on a separate local memory storage device or remotely. If the patient data added in the patient text boxes 536 is for a new patient, the user can select the add new patient button 552 to add the new patient to the patient database. The patients in the patient database can also be reviewed in a scroll box 548. A scroll control 550 allows up and down scrolling of the patient database records. The patient database records are shown as being sorted by last name, but may be sortable by any of the patient fields in the patient database.

If a patient is selected in the scroll box 548, which may be an existing or just newly added patient, as illustrated in the GUI screen 560 in FIG. 42, the user is provided with an option to either capture new tear film images of the selected patient or to view past images, if past tear film images are stored for the selected patient on disk memory 268. In this regard, the selected patient is highlighted 562 in the patient scroll box 548, and a select patient action pop-up box 564 is displayed. The user can either select the capture new images button 566 or the view past images button 568. If the capture new images button 566 is selected, the capture images GUI 570 is displayed to the user under the capture images tab 571 on the display 174, which is illustrated in FIG. 43. As illustrated therein, a patient eye image viewing area 572 is provided, which is providing images of the patient's eye and tear film obtained by the video camera 198 in the OSI device 170. In this example, the image is of the patient's tear film onto the raw image of the patient's eye and tear film, as previously discussed. The focus of the image can be adjusted via a focus control 574. The brightness level of the image in the viewing area 572 is controlled via a brightness control 576. The user can control the position of the video camera 198 to align the camera lens with the tear film of interest whether the lens is aligned with the patient's left or right eye via an eye selection control 578. Each frame of the patient's eye captured by the video camera 198 can be stepped via a stepping control 580. Optionally, or in addition, a joystick may be provided in the OSI device 170 to allow control of the video camera 198.

The stored images of the patient's eye and tear film can also be accessed from a patient history database stored in disk memory 268. FIG. 44 illustrates a patient history GUI screen 582 that shows a pop-up window 584 showing historical entries for a given patient. For each tear film imaging, a time and date stamp 585 is provided. The images of a patient's left and right eye can be shown in thumbnail views 586, 588 for ease in selection by a user. The stored images can be scrolled up and down in the pop-up window 584 via a step scroll bar 590. Label names in tag boxes 592 can also be associated with the images. Once a desired image is selected for display, the user can select the image to display the image in larger view in the capture images GUI 570 in FIG. 43. Further, two tear film images of a patient can be simultaneously displayed from any current or prior examinations for a single patient, as illustrated in FIG. 45.

As illustrated in FIG. 45, a view images GUI screen 600 is shown, wherein a user has selected a view images tab 601 to display images of a patient's ocular tear film. In this view images GUI screen 600, both images of the patient's left eye 602 and right eye 604 are illustrated side by side. In this example, the images 602, 604 are images of the patients tear film onto the raw image of the patient's tear eye and tear film, as previously discussed. Scroll buttons 606, 608 can be selected to move a desired image among the video of images of the patient's eye for display in the view images GUI screen 600. Further, step and play controls 610, 612 allow the user to control playing a stored video of the patient's tear film images and stepping through the patient's tear film images one at a time, if desired. The user can also select an open patient history tab 614 to review information stored regarding the patient's history, which may aid in analysis and determining whether the patient's tear film has improved or degraded. A toggle button 615 can be selected by the user to switch the images 602, 604 from the overlay view to just the images 620, 622, of the resulting interference interactions of specularly reflected light from the patient's tear films, as illustrated in FIG. 46. As illustrated in FIG. 46, only the resulting interference interactions from the patient's tear film are illustrated. The user may select this option if it is desired to concentrate the visual examination of the patient's tear film solely to the interference interactions.

Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. These modifications include, but are not limited to, the type of light source or illuminator, the type of imaging device, image device settings, the relationship between the illuminator and an imaging device, the control system, the type of tear film interference model, and the type of electronics or software employed therein, the display, the data storage associated with the OSI device for storing information, which may also be stored separately in a local or remotely located remote server or database from the OSI device, any input or output devices, settings, including pre-processing and post-processing settings. Further, the present invention is not limited to illumination of any particular area on the patient's tear film or use of any particular color value representation scheme.

Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

What is claimed is:
 1. An apparatus for imaging an ocular tear film, comprising: a light source configured to direct a light including unpolarized light having a first intensity in an illumination path to illuminate a region of interest (ROI) of an ocular tear film, thereby producing a specularly reflected light in a first polarization plane containing optical wave interference from the ROI of the ocular tear film; a polarizer disposed in the illumination path having a polarization axis parallel or substantially parallel to the first polarization plane of the specularly reflected light to cause a background signal comprised of unpolarized light returned from the ROI of the ocular tear film to have a second intensity less than the first intensity; an imaging device configured to capture the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film.
 2. The apparatus of claim 1, wherein the light source is multi-wavelength.
 3. The apparatus of claim 2, wherein a control system is configured to receive at least one image containing the optical wave interference of specularly reflected light and the background signal captured by the imaging device while illuminated by multi-wavelength light passing through the polarizer.
 4. The apparatus of claim 1, wherein background subtraction is not utilized to reduce the background signal.
 5. The apparatus of claim 1, wherein the polarizer attenuates the unpolarized light thereby increasing a ratio of the specularly reflected light to the background signal comprised of the unpolarized light returned from the ROI of the ocular tear film.
 6. The apparatus of claim 1, wherein the background signal includes unpolarized light from the ocular tear film comprising at least a portion of the background signal.
 7. The apparatus of claim 1, wherein the polarizer decreases the first intensity of the background signal comprised of unpolarized light returned from the ROI of the ocular tear film as compared to the first intensity of the background signal if the polarizer were not disposed in the illumination path.
 8. The apparatus of claim 1, further comprising a second polarizer disposed in an imaging path of the imaging device.
 9. The apparatus of claim 8, wherein the second polarizer has a polarization axis aligned parallel or substantially parallel with the specularly reflected light in the first polarization plane from the ROI of the ocular tear film.
 10. The apparatus of claim 8, wherein unpolarized light making up a background signal is reduced by at least 50 percent compared to utilization of the first polarizer alone.
 11. The apparatus of claim 8, wherein a ratio of specularly reflected light intensity from the ocular tear film to background signal intensity is at least 400 percent.
 12. The apparatus of claim 8, wherein the second polarizer is held by a rotatable holder such that the second polarizer is selectively disposable between a first position within an imaging path of the imaging device and a second position outside the imaging path of the imaging device.
 13. The apparatus of claim 12, wherein the rotatable holder is coupled to an electric motor that is usable to selectively dispose the second polarizer between the first position and the second position.
 14. The apparatus of claim 1, further comprising: a polarizer disposed in an illumination path between the multi-wavelength light source and the ocular tear film, wherein the polarizer has a polarization axis that is parallel or substantially parallel to the first polarization plane of the specularly reflected light from the ROI of the ocular tear film; and a second polarizer disposed in an imaging path of the imaging device, wherein the second polarizer has a polarization axis that is parallel or substantially parallel to the first polarization plane of the specularly reflected light from the ROI of the ocular tear film.
 15. The apparatus of claim 14, wherein randomly polarized light making up a background signal is reduced by at least 50 percent compared to utilization of the polarizer alone.
 16. The apparatus of claim 14, wherein a ratio of specularly reflected light intensity from the ocular tear film to background signal intensity is at least 400 percent.
 17. The apparatus of claim 1, wherein the background signal includes at least one of stray light and ambient light.
 18. The apparatus of claim 1, wherein the multi-wavelength light source is comprised of a multi-wavelength Lambertian light source configured to uniformly or substantially uniformly illuminate the ROI of the ocular tear film.
 19. The apparatus of claim 1, wherein polarizer is a circular polarizer.
 20. The apparatus of claim 1, wherein the control system is further configured to display the at least one image on a visual display.
 21. A method of imaging an ocular tear film, comprising: directing multi-wavelength light including unpolarized light having a first intensity in an illumination path to illuminate a region of interest (ROI) of an ocular tear film thereby producing a specularly reflected light in a first polarization plane containing optical wave interference from the ROI of the ocular tear film; polarizing the unpolarized light to cause a background signal comprised of unpolarized light returned from the ROI of the ocular tear film to have a second intensity less than the first intensity; capturing at least one image of the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film; and receiving the at least one image containing the optical wave interference of specularly reflected light and the background signal.
 22. An apparatus for imaging an ocular tear film, comprising: a multi-wavelength light source configured to direct a multi-wavelength light including unpolarized light having a first intensity in an illumination path to illuminate a region of interest (ROI) of an ocular tear film, thereby producing a specularly reflected light in a first polarization plane containing optical wave interference from the ROI of the ocular tear film; a polarizer disposed in the illumination path having a polarization axis parallel or substantially parallel to the first polarization plane of the specularly reflected light to cause a background signal comprised of unpolarized light returned from the ROI of the ocular tear film to have a second intensity less than the first intensity; an imaging device configured to capture the optical wave interference of specularly reflected light and the background signal from the ROI of the ocular tear film; and a control system configured to receive at least one image containing the optical wave interference of specularly reflected light and the background signal captured by the imaging device while illuminated by multi-wavelength light passing through the polarizer.
 23. The apparatus of claim 22, wherein background subtraction is not utilized to reduce the background signal.
 24. The apparatus of claim 22, wherein the polarizer attenuates the unpolarized light thereby increasing a ratio of the specularly reflected light to the background signal comprised of the unpolarized light returned from the ROI of the ocular tear film.
 25. The apparatus of claim 22, wherein the background signal includes unpolarized light from the ocular tear film comprising at least a portion of the background signal.
 26. The apparatus of claim 22, wherein the polarizer decreases the first intensity of the background signal comprised of unpolarized light returned from the ROI of the ocular tear film as compared to the first intensity of the background signal if the polarizer were not disposed in the illumination path.
 27. The apparatus of claim 22, further comprising a second polarizer disposed in an imaging path of the imaging device.
 28. The apparatus of claim 27, wherein the second polarizer has a polarization axis aligned parallel or substantially parallel with the specularly reflected light in the first polarization plane from the ROI of the ocular tear film.
 29. The apparatus of claim 27, wherein unpolarized light making up a background signal is reduced by at least 50 percent compared to utilization of the first polarizer alone.
 30. The apparatus of claim 27, wherein a ratio of specularly reflected light intensity from the ocular tear film to background signal intensity is at least 400 percent.
 31. The apparatus of claim 27, wherein the second polarizer is held by a rotatable holder such that the second polarizer is selectively disposable between a first position within an imaging path of the imaging device and a second position outside the imaging path of the imaging device.
 32. The apparatus of claim 31, wherein the rotatable holder is coupled to an electric motor that is usable to selectively dispose the second polarizer between the first position and the second position.
 33. The apparatus of claim 22, further comprising: a polarizer disposed in an illumination path between the multi-wavelength light source and the ocular tear film, wherein the polarizer has a polarization axis that is parallel or substantially parallel to the first polarization plane of the specularly reflected light from the ROI of the ocular tear film; and a second polarizer disposed in an imaging path of the imaging device, wherein the second polarizer has a polarization axis that is parallel or substantially parallel to the first polarization plane of the specularly reflected light from the ROI of the ocular tear film.
 34. The apparatus of claim 33, wherein randomly polarized light making up a background signal is reduced by at least 50 percent compared to utilization of the polarizer alone.
 35. The apparatus of claim 33, wherein a ratio of specularly reflected light intensity from the ocular tear film to background signal intensity is at least 400 percent.
 36. The apparatus of claim 22, wherein the background signal includes at least one of stray light and ambient light.
 37. The apparatus of claim 22, wherein the multi-wavelength light source is comprised of a multi-wavelength Lambertian light source configured to uniformly or substantially uniformly illuminate the ROI of the ocular tear film.
 38. The apparatus of claim 22, wherein polarizer is a circular polarizer.
 39. The apparatus of claim 22, wherein the control system is further configured to display the at least one image on a visual display. 